Charging system providing adjustable transmitted power to improve power efficiency within an implanted device

ABSTRACT

A system for transferring power to, and communicating with, at least one body-implantable active device includes an external power transfer system associated with an external device disposed outside of a body, operable to transfer power through a dermis layer to each body-implantable active device, and communicate data to and from each body-implantable active device, and also includes a power receiving system associated with each body-implantable active device, operable to receive power transferred from the external power transfer system, and communicate data to and from the external power transfer system. The body-implantable active device may include an implantable neurostimulation system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/989,706, filed Jan. 6, 2016, entitled CHARGING SYSTEM INCORPORATINGINDEPENDENT CHARGING AND COMMUNICATION WITH MULTIPLE IMPLANTED DEVICES,the specification of which is incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The present disclosure relates to systems and methods for wirelesslycharging/powering and communicating with body-implantable active medicaldevices, and particularly for a body-implantable neurostimulationdevice.

BACKGROUND

Neurostimulation systems that include implantable neurostimulation leadsare used to treat chronic pain. Such systems may include an implantablepulse generator (IPG) from which one or more neurostimulating leads mayextend to a length sufficient to provide therapeutic neurostimulationover desired regions of the body, such as regions of the head and back.The IPG may include a rechargeable battery, an antenna coil, andcircuitry to control the neurostimulating leads. The IPG may also beconfigured for functionally connecting with an external radiofrequencyunit that may be operable to perform various functions includingrecharging the rechargeable battery, diagnostically evaluating the IPG,and programming the IPG.

Improved techniques are desired for wirelessly charging/powering andcommunicating with such implantable neurostimulation systems and otherbody-implantable active devices, especially when such systems areimplanted fully beneath the skin.

SUMMARY

In one aspect, a system is provided for transferring power to, andcommunicating with, at least one body-implantable active device. In someembodiments the system includes an external power transfer systemassociated with an external device disposed outside of a body, operableto transfer power through a dermis layer to each body-implantable activedevice, and communicate data to and from each body-implantable activedevice, and also includes a power receiving system associated with eachbody-implantable active device, operable to receive power transferredfrom the external power transfer system, and communicate data to andfrom the external power transfer system.

In another aspect, a system is provided for charging and communicatingwith at least two body-implanted active devices, each with a battery. Insome embodiments, the system includes an external charging systemdisposed outside of the body for transferring charging energy to thebody and facilitating transmission of data to, and reception of datafrom, the body-implanted active devices, and also includes a chargereceiving system associated with each of the body-implanted activedevices for receiving energy transferred from the external chargingsystem and facilitating transmission of data to, and reception of datafrom, the external charging system.

In various implementations, the body-implanted active device may includean implantable head-located, unibody peripheral nerve stimulation systemthat is configured for implantation of substantially all electronics,including an on-site battery, at or near the implanted electrodes on theskull. The system may include an implantable pulse generator (IPG) fromwhich two neurostimulating leads may extend to a length sufficient toprovide therapeutic neurostimulation unilaterally over the frontal,parietal and occipital regions of the hemicranium. The system may beoperable to provide medically acceptable therapeutic neurostimulation tomultiple regions of the head, including the frontal, parietal andoccipital regions of the hemicranium, substantially simultaneously.

Each of the leads may include an extended lead body, a plurality ofsurface metal electrodes disposed along the lead body, which electrodesmay be divided into two or more electrode arrays, and a plurality ofinternal electrically conducting metal wires running along at least aportion of the length of the lead body and individually connecting aninternal circuit of the IPG to individual surface metal electrodes. Theextended lead body may comprise a medical grade plastic. The IPG mayinclude a rechargeable battery, an antenna coil, and an applicationspecific integrated circuit (ASIC). The IPG may be configured forfunctionally connecting with an external radiofrequency control device.The external radiofrequency control device may be operable to performvarious functions including recharging the rechargeable battery,diagnostically evaluating the IPG, and programming the IPG.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail. The details ofvarious implementations are set forth in the accompanying drawings andthe description below. Consequently, those skilled in the art willappreciate that the foregoing summary is illustrative only and is notintended to be in any way limiting of the invention. It is only theclaims, including all equivalents, in this or any non-provisionalapplication claiming priority to this application, that are intended todefine the scope of the invention(s) supported by this application.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following description, taken in conjunction with theaccompanying drawings.

FIG. 1 is a block diagram of a system that provides for independentcharging and communication with multiple implanted devices, inaccordance with some embodiments of the invention.

FIG. 2 is a block diagram of a system depicting the de-tuning of areceive coil within an implanted device to selectively turn offcharging, in accordance with some embodiments of the invention.

FIG. 3 is a block diagram of a system which provides for datacommunication (forward telemetry) and power transmission to an implanteddevice using opposite polarity half-wave rectified signals received bythe implanted device, in accordance with some embodiments of theinvention.

FIG. 4A is a block diagram of a system which provides for bi-directionalcommunication with an implanted device, and particularly illustratespassive communication from an implanted device (back telemetry) when thereceive coil is de-tuned, in accordance with some embodiments of theinvention.

FIG. 4B illustrates voltage waveforms of selected signals depicted inthe embodiment shown in FIG. 4A.

FIG. 5A is a block diagram of a system which includes transmit coilcurrent sensing circuitry to determine back telemetry data received froman implanted device, and to determine de-tuning of an implanted devicecoil, in accordance with some embodiments of the invention.

FIG. 5B illustrates voltage waveforms of selected signals depicted inthe embodiment shown in FIG. 5A.

FIG. 6 is a block diagram of a system which provides for adjustabletransmitted power to improve power efficiency within an implanteddevice, in accordance with some embodiments of the invention.

FIG. 7A is a block diagram of a system which includes feedbackexcitation control of a resonant coil driver amplifier, in accordancewith some embodiments of the invention.

FIG. 7B illustrates voltage waveforms of selected signals depicted inthe embodiment shown in FIG. 7A.

FIG. 8 is a block diagram of a headset that includes an externalcharging system for two implanted devices, in accordance with someembodiments of the invention.

FIG. 9, which includes FIGS. 9A and 9B, is a schematic diagram of anexemplary IPG driver and telemetry circuitry block, such as that shownin FIG. 8, in accordance with some embodiments of the invention.

FIGS. 10A, 10B, and 10C illustrate voltage waveforms of selected signalsdepicted in the embodiment shown in FIG. 9 and FIG. 13A.

FIG. 11 is a schematic diagram of an exemplary headset buck/boostvoltage generator circuit, such as that shown in FIG. 8, in accordancewith some embodiments of the invention.

FIG. 12 is a block diagram of a body-implantable active device, inaccordance with some embodiments of the invention.

FIG. 13A is a schematic diagram of an exemplary rectifier circuit andtelemetry/de-tune circuit, such as those shown in FIG. 12, in accordancewith some embodiments of the invention.

FIG. 13B illustrates voltage waveforms of selected signals depicted inthe embodiment shown in FIG. 13A.

FIG. 14 is a schematic diagram of portions of an exemplary boostcircuit, such as that shown in FIG. 12, in accordance with someembodiments of the invention.

FIG. 15 is a diagram representing an exemplary headset that includes anexternal charging system for two separate body-implantable devices, eachimplanted behind a patient's respective left and right ears, and showsan associated headset coil placed in proximity to the correspondingreceive coil in each implanted device.

FIG. 16 depicts a side view of a head-located, unibody neurostimulatorsystem for migraine and other head pain. The system includes animplantable pulse generator (IPG) from which two neurostimulating leadsextend. Each lead includes a plurality of electrodes in a distributionand over a length to allow full unilateral coverage of the frontal,parietal, and occipital portions of the head.

FIG. 17 depicts a side view of one of the neurostimulating leads shownin FIG. 16, and illustrates a surface electrode array. Each electrode ofthe array is connected to a corresponding internal wire within theneurostimulating lead.

FIG. 18 depicts a side view of the internal wires exiting from the IPG'sinternal circuit en route to surface electrodes disposed over the twoneurostimulating leads.

FIG. 19 depicts a side view of a head with a full head-locatedneurostimulator system in-situ.

In the drawings, like reference numbers are used herein to designatelike elements throughout. The drawings are not necessarily drawn toscale, and in some instances the drawings have been exaggerated and/orsimplified in places for illustrative purposes only.

DETAILED DESCRIPTION

Embodiments will now be described more fully hereinafter with referenceto the accompanying drawings, in which various embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete. One of ordinaryskill in the art will appreciate the many possible applications andvariations based on the following examples of possible embodiments.

FIG. 1 depicts a conceptual diagram of a system 500 that provides forindependent charging/powering and communication with multiplebody-implanted devices requiring external power to power thebody-implanted devices directly or to charge an internal battery (orother charge storage device) associated with the body-implanted devices,or a hybrid thereof. For the purposes of this disclosure, chargeprovided to the body-implanted devices will be referred to as“charging,” but it should be understood that this could mean charging ofa battery or other charge storage device, or delivering charge to powera circuit block or element associated with the body-implanted devices,or a combination of both. Three charge receiving systems 520, 540, 560are shown, each disposed within a corresponding body-implanted device(not shown). An external charging system 502 disposed outside a dermislayer 518 includes series-connected transmit coils, of which three areshown, being series-connected transmit coils 510, 511, 512, each ofwhich corresponds to a respective one of receive coils 521, 541, 561 ofrespective ones of a plurality of charge receiving systems, of whichthree are shown, being charge receiving systems 520, 540, 560.Preferably each receive coil 521, 541, 561 is tuned to the resonantfrequency of the respective transmit coil 510, 511, 512 within theexternal charging system 502. While three transmit coils 510, 511, 512are shown, one for each charge receiving system 520, 540, 560, otherembodiments may utilize one transmit coil, two transmit coils, oranother number of transmit coils, depending upon the number ofbody-implanted devices.

The external charging system 502 includes a driver 504, responsive to aDRIVER CTRL signal on node 503, for driving the series-connected coils510, 511, 512 with an AC signal. A TX/RX telemetry block 506 includes atransmitter for transmitting a forward telemetry data signal within theAC signal driven across the transmit coils (i.e., on node 508), and areceiver to detect and receive a back telemetry data signal within theAC signal. The forward/back telemetry data signals, both as representedby the DATA signal on node 505, are coupled from/to telemetry circuitrywithin remaining portions of the external charging system (not shown).As used herein, data communication from an external charging system to abody-implanted device is referred to as forward telemetry, and datacommunication from a body-implanted device to an external chargingsystem is referred to as back telemetry.

Within the first body-implanted device, the charge receiving system 520includes a receive coil 521 that is tuned to the resonant frequency ofthe associated transmit coil 510 within the external charging system502, so that receive coil 521 may receive energy transferred from thetransmit coil 510 when in close proximity thereto. The receive coil 521is coupled to a charge receiving block 528 that includes circuitry forreceiving energy in a first mode of operation, and for de-tuning thereceive coil 521 in a second mode of operation to inhibit transfer ofenergy. The receive coil 521 is also coupled (via node 522) to an RX/TXtelemetry block 523 that includes a receiver for receiving a forwardtelemetry data signal from the receive coil 521, and a transmitter fortransmitting a back telemetry data signal to the receive coil 521. Thereceived energy is coupled to battery charging circuitry, and theforward/back telemetry data signals are coupled to/from data circuitrywithin the first body-implanted device, both as represented by node 529.As can be appreciated, the receive coil 521 serves as a “shared antenna”for both the charging system and the telemetry system.

Similarly, the charge receiving system 540 includes a receive coil 541that is tuned to the resonant frequency of the associated transmit coil511, so that receive coil 541 may receive energy transferred from thetransmit coil 511 when in close proximity thereto. The receive coil 541is coupled to a charge receiving block 548 that includes circuitry forreceiving energy in the first mode of operation, and for de-tuning thereceive coil 541 in the second mode of operation to inhibit transfer ofenergy. The receive coil 541 is also coupled (via node 542) to an RX/TXtelemetry block 543 that includes a receiver for receiving a forwardtelemetry data signal from the receive coil 541, and a transmitter fortransmitting a back telemetry data signal to the receive coil 541. Thereceived energy is coupled to battery charging circuitry (or a chargedelivering circuit when no battery is present), and the forward/backtelemetry data signals are coupled to/from data circuitry within thesecond body-implanted device, both as represented by node 549.

Likewise, the charge receiving system 560 includes a receive coil 561that is tuned to the resonant frequency of the associated transmit coil512, so that receive coil 561 may receive energy transferred from thetransmit coil 512 when in close proximity thereto. The receive coil 561is coupled to a charge receiving block 568 that includes circuitry forreceiving energy in the first mode of operation, and for de-tuning thereceive coil 561 in the second mode of operation to inhibit transfer ofenergy. The receive coil 561 is also coupled (via node 562) to an RX/TXtelemetry block 563 that includes a receiver for receiving a forwardtelemetry data signal from the receive coil 561, and a transmitter fortransmitting a back telemetry data signal to the receive coil 561. Thereceived energy is coupled to battery charging circuitry, and theforward/back telemetry data signals are coupled to/from data circuitrywithin the third body-implanted device, both as represented by node 569.

Even though a single driver circuit 504 is utilized to drive all threeseries-connected transmit coils 510, 511, 512, the system 500 providesfor independent charging (or charge delivery) of multiple body-implanteddevices. When such charging of one of the body-implanted devices iscomplete (or delivery of charge), the corresponding de-tuning circuitrywithin the respective charge receiving circuit 528, 548, 568 may beactivated to de-tune its respective receive coil 521, 541, 561 andthereby inhibit further transfer of energy to the respective chargereceiving circuit 528, 548, 568. Each body-implanted device may de-tuneits receive coil when charging is complete, independently of the otherbody-implanted devices, to limit needless power loss and undesirableheating within a fully-charged body-implanted device (or a non-batterydevice that requires no delivery of charge), without affecting energytransfer to the remaining charge receiving systems 520, 540, 560.

Moreover, even though a single driver circuit 504 is utilized to driveall three series-connected transmit coils 510, 511, 512, the system 500also provides for independent communication with multiple body-implanteddevices. Since the forward telemetry (transmit) data signal within theAC signal is driven across all three series-connected transmit coils501, 511, 512, each of the charge receiving systems 520, 540, 560 canindependently receive such a transmitted data signal. As for receivingdata independently from each charge receiving system, the externalcharging system 502 can coordinate the operation of each chargereceiving system 520, 540, 560 so that only one such charge receivingsystem at a time attempts to communicate back telemetry data to theexternal charging system 502. Such coordination may be achieved byforward telemetry commands instructing a selected charge receivingsystem to communicate back telemetry data to the external chargingsystem 502, so that the non-selected charge receiving systems willforego attempted back telemetry during such times. Embodiments describedbelow provide detailed examples of forward and back telemetry circuitryand operation.

FIG. 2 is a block diagram of a system 600 that provides for thede-tuning of a receive coil within a given body-implanted device toselectively turn off charging (charge delivery) of the given devicewithout affecting battery charging (charge delivery) in one or moreother such body-implanted devices. Two charge receiving systems 620, 630are shown, each disposed within a corresponding body-implanted device.An external charging (charge delivery) system 610 disposed outside adermis layer 602 includes series-connected transmit coils 612, 613, eachof which corresponds to a respective one of receive coils 621, 631 ofrespective charge receiving systems 620, 630. In this embodiment, twosuch transmit coils 612, 613 are shown, one for each charge receivingsystem 620, 630, but other embodiments may utilize one transmit coil oranother number of transmit coils, depending upon the number ofbody-implanted devices.

The external charging system 610 includes a driver 611, responsive to aCTRL signal, for driving the series-connected transmit coils 612, 613with an AC signal. Within the first body-implanted device, the chargereceiving system 620 includes a receive coil 621 that is preferablytuned to the resonant frequency of the associated transmit coil 612within the external charging system 610, so that receive coil 621 mayreceive energy transferred from the transmit coil 612 when in closeproximity thereto. The receive coil 621 is coupled to a rectifier block622 for receiving energy in a first mode of operation and generating arectified voltage on node 624, and for de-tuning the receive coil 621 ina second mode of operation, responsive to a DE-TUNE signal on node 623,to inhibit transfer of energy. The rectified voltage on node 624 iscoupled to battery charging (charge delivery) circuitry within the firstbody-implanted device (not shown).

Within the second body-implanted device, the charge receiving system 630includes a receive coil 631 that is preferably tuned to the resonantfrequency of the associated transmit coil 613 within the externalcharging system 610, so that receive coil 631 may receive energytransferred from the transmit coil 613 when in close proximity thereto.The receive coil 631 is coupled to a rectifier block 632 for receivingenergy in the first mode of operation and generating a rectified voltageon node 634, and for de-tuning the receive coil 631 in the second modeof operation, responsive to a DE-TUNE signal on node 633, to inhibittransfer of energy. The rectified voltage on node 634 is coupled tobattery charging (charge delivery) circuitry within the secondbody-implanted device (not shown).

Even though a single driver circuit 611 is utilized to drive bothseries-connected transmit coils 612, 613, the system 600 provides forde-tuning of a receive coil within a given body-implanted device toselectively turn off charging of the given device without affectingcharging of one or more other such body-implanted devices. As such,independent charging (charge delivery) of multiple body-implanteddevices is provided. When such charging (charge delivery) of one of thebody-implanted devices is complete, the corresponding DE-TUNE signal maybe activated within the respective charge receiving system 620, 630 tode-tune its respective receive coil 621, 631 and thereby inhibittransfer of energy to the respective charge receiving system 620, 630.Each body-implanted device may de-tune its receive coil when charging(charge delivery) is complete, independently of the other body-implanteddevices, to limit needless power loss and undesirable heating within afully-charged body-implanted device, without affecting energy transferto the remaining charge receiving systems 620, 630. Such completion ofcharging (charge delivery) may be determined within the charge receivingsystem of the respective body-implanted device, with or without anycommunication to the external charging system.

FIG. 3 is a block diagram of a system 645 which provides for powertransmission and data communication to a body-implanted device usingopposite-polarity half-wave rectified signals received by the implanteddevice. Two charge receiving systems 650, 660 are shown, each disposedwithin a corresponding body-implanted device. An external chargingsystem 640 disposed outside a dermis layer 602 includes series-connectedtransmit coils 642, 643, each of which corresponds to a respective oneof receive coils 651, 661 of respective charge receiving systems 650,660. Preferably each receive coil 651, 661 is tuned to the resonantfrequency of the respective transmit coil 642, 643 within the externalcharging system 640. In this embodiment, two such transmit coils 642,643 are shown, one for each charge receiving system 650, 660, but otherembodiments may utilize one transmit coil or another number of transmitcoils.

The external charging system 640 includes a driver 641 that isresponsive to a forward telemetry transmit data signal FWD TELEM TXDATA. When the FWD TELEM TX DATA signal has a first logic state (e.g.,logic high), the driver 641 drives the series-connected transmit coils642, 643 with an AC signal, and when the FWD TELEM TX DATA signal has asecond logic state (e.g., logic low), the driver 641 is disabled. Insome embodiments, the driver 641 together with the series-connectedtransmit coils 642, 643 may be configured as a resonant amplifier. Whensuch a resonant amplifier is disabled, the AC signal is allowed to decayand eventually cease.

Such operation may be viewed as providing a 100% amplitude-modulated ACsignal driven across the series-connected transmit coils 642, 643,controlled by a bit-serial forward telemetry data signal FWD TELEM TXDATA. Significant charge transfer to one or both charge receivingsystems 650, 660 is still readily provided for battery charging (orcharge delivery) by limiting the duration of time that the forwardtelemetry transmit data signal FWD TELEM TX DATA is allowed to “disable”the coil driver 641. Consequently, such a signal also functions as anenable/disable signal for the driver 641 if maintained in the secondlogic state.

Within a first body-implanted device, the charge receiving system 650includes a receive coil 651 for receiving energy transferred from theassociated transmit coil 642 when in close proximity thereto. Thereceive coil 651 is coupled to a positive half-wave rectifier block 653for receiving energy and generating a rectified voltage on node 654, andresponsive to a DE-TUNE signal on node 655, for de-tuning the receivecoil 651 to inhibit transfer of energy from the associated transmit coil642. The rectified voltage on node 654 is coupled to power and batterycharging (charge delivery) circuitry within the first body-implanteddevice (not shown), which circuitry also directly or indirectly controlsthe DE-TUNE signal on node 655 when charging is complete or chargetransfer not desired. The receive coil 651 is also coupled via node 657to a negative half-wave rectifier block 652 for receiving forwardtelemetry data and generating on node 656 a respective forward telemetryreceive data signal, which is conveyed to forward telemetry receive dataFWD TELEM RX DATA circuitry within the first body-implanted device (notshown).

Within a second body-implanted device, the charge receiving system 660includes a receive coil 661 for receiving energy transferred from theassociated transmit coil 643 when in close proximity thereto. Thereceive coil 661 is coupled to a positive half-wave rectifier block 663for receiving energy and generating a rectified voltage on node 664, andresponsive to a DE-TUNE signal on node 665, for de-tuning the receivecoil 661 to inhibit transfer of energy from the associated transmit coil643. The rectified voltage on node 664 is coupled to power and batterycharging circuitry within the second body-implanted device (not shown),which circuitry also directly or indirectly controls the DE-TUNE signalon node 665 when charging is complete or charge transfer not desired.The receive coil 661 is also coupled via node 667 to a negativehalf-wave rectifier block 662 for receiving forward telemetry data andgenerating on node 666 a respective forward telemetry receive datasignal, which is conveyed to forward telemetry receive data FWD TELEM RXDATA circuitry within the first body-implanted device (not shown).

As may be appreciated, each body-implanted device can receive forwardtelemetry data independently, irrespective of the charging state (i.e.,de-tuned state) of that body-implanted device or the otherbody-implanted device. For example, the charge receiving system 650 maystill receive forward telemetry information by the negative half-waverectifier 652 irrespective of whether the positive half-wave rectifier653 is de-tuned or not. Such de-tuning greatly lowers the resonant Q ofthe combination of transmit coil 642 and receive coil 651 for positivevoltage excursions on node 657, and consequently serves to inhibitsignificant energy transfer to receive coil 651, but does not negativelyimpact the ability for the negative half-wave rectifier 652 to respondto negative transitions on node 657 and generate the output voltageaccordingly on node 656. Similarly, the charge receiving system 650 maystill receive forward telemetry information irrespective of whether thepositive half-wave rectifier 663 within the other charge receivingsystem 660 is de-tuned or not.

FIG. 4A is a block diagram of a system 675 which provides forbi-directional communication with a body-implanted device, andparticularly illustrates passive communication from an implanted deviceto the external charging system (i.e., back telemetry) when the receivecoil within the implanted device is de-tuned.

Two charge receiving systems 680, 690 are shown, each disposed within acorresponding body-implanted device. An external charging system 670disposed outside a dermis layer 602 includes series-connected transmitcoils 673, 674, each of which corresponds to a respective one of receivecoils 681, 691 of respective charge receiving systems 680, 690. Asbefore, preferably each receive coil 681, 691 is tuned to the resonantfrequency of the respective transmit coil 673, 674 within the externalcharging system 670. In this embodiment, two such transmit coils 673,674 are shown, one for each charge receiving system 680, 690, but otherembodiments may utilize one transmit coil or another number of transmitcoils, noting that the transmit coils are for delivery of charge to thebody-implanted devices. Such charge delivery may be utilized to charge abattery, capacitor, or supercapacitor within the body-implanted device,and/or to power the body-implanted device, particularly if suchbody-implanted device does not include a battery.

The external charging (charge delivery) system 670 includes a driver 671that is responsive to a forward telemetry transmit data signal FWD TELEMTX DATA. As described in the embodiment shown in FIG. 3, when the FWDTELEM TX DATA signal is driven to a first logic state (e.g., logichigh), the driver 671 drives the series-connected transmit coils 673,674 with an AC signal, and when the FWD TELEM TX DATA signal is drivento a second logic state (e.g., logic low), the driver 671 is disabled.In some embodiments, the driver 671 together with the series-connectedtransmit coils 673, 674 may be configured as a resonant amplifier. Whensuch a resonant amplifier is disabled, the AC signal decays andeventually ceases. Such operation may be viewed as providing a 100%amplitude modulation of the AC signal driven onto the series-connectedtransmit coils 673, 674, which modulation is controlled by a bit-serialforward telemetry data signal that also functions as an enable/disablesignal for the driver 671 (if held to the appropriate one of its twologic states). The external charging system 670 also includes a receivercircuit 672 that is responsive to the AC signal on the series-coupledtransmit coils 673, 674, and which generates accordingly a backtelemetry receive data signal BACK TELEM RX DATA.

Within a first body-implanted device, the charge receiving system 680includes a receive coil 681 for receiving energy transferred from theassociated transmit coil 673 when in close proximity thereto. Thereceive coil 681 is coupled to a positive half-wave rectifier block 683for receiving energy and generating a rectified voltage on node 684, andresponsive to a DE-TUNE signal on node 685, for de-tuning the receivecoil 681 to inhibit transfer of energy from the associated transmit coil673. The rectified voltage on node 684 is coupled to power and batterycharging circuitry within the first body-implanted device (not shown).The receive coil 681 is also coupled via node 687 to a negative peakdetector block 682 for receiving forward telemetry data and generatingon node 686 a respective forward telemetry receive data signal, which isconveyed to forward telemetry receive data FWD TELEM RX DATA circuitrywithin the first body-implanted device (not shown).

The charge receiving system 680 also includes a de-tune control block688 for generating the DE-TUNE control signal on node 685 responsive toa disable power transfer signal DISABLE PWR TRANSFER, and furtherresponsive to a bit-serial back telemetry transmit data signal BACKTELEM TX DATA. In operation, the DISABLE PWR TRANSFER signal may beasserted when charging (or charge transfer) is complete or not desired,which asserts the DE-TUNE control signal to de-tune the receive coil 681through the positive half-wave rectifier 683. In addition, during normalcharging the DE-TUNE control signal may be asserted for eachbit-position of the bit-serial BACK TELEM TX DATA signal correspondingto one of its two data states. Since de-tuning the positive half-waverectifier 683 in concert with the receive coil 681 inhibits energytransfer from the transmit coil 673 to the receive coil 681, the loadingof transmit coil 673 is decreased. This decreased loading results in ahigher peak current through the series-connected transmit coils 673,674. In the external charging system 670, the receiver circuit 672senses the change in peak current through the series-coupled transmitcoils 673, 674 as each serial data bit of the BACK TELEM TX DATA signaleither tunes or de-tunes the receive coil 681, and generates accordinglya back telemetry receive data signal BACK TELEM RX DATA.

If the DE-TUNE control signal is already asserted (e.g., because theDISABLE PWR TRANSFER signal is asserted to indicate charging/chargetransfer is complete or not desired) when the charge receiving system680 desires to transmit back telemetry data, the DISABLE PWR TRANSFERsignal may be briefly de-asserted to allow the BACK TELEM TX DATA signalto control the DE-TUNE control signal, as is shown in FIG. 4B. Thus, thecharge receiving system 680 may still transmit back telemetryinformation irrespective of whether it is generally in a de-tuned state.

Within a second body-implanted device, the charge receiving system 690includes a receive coil 691 for receiving energy transferred from theassociated transmit coil 674 when in close proximity thereto. Theremainder 692 of the charge receiving system 690 is identical to thecharge receiving system 680, and need not be separately described.

FIG. 5A is a block diagram of a system 701 which includes transmit coil(“charging coil”) current sensing circuitry, and particularlyillustrates sensing such transmit coil current to determine backtelemetry data received from an implanted device, and to determinede-tuning of an implanted device receive coil. Two charge receivingsystems 720, 730 are shown, each disposed within a correspondingbody-implanted active device. An external charging system 700 disposedoutside a dermis layer 602 includes series-connected transmit coils 703,704, each of which corresponds to a respective one of receive coils 721,731 of respective charge receiving systems 720, 730. Although two suchtransmit coils 703, 704 are shown, one for each charge receiving system720, 730, other embodiments may utilize one transmit coil or anothernumber of transmit coils, depending upon the number of body-implanteddevices.

The external charging system 700 includes a driver 702, responsive to aCTRL signal, for driving the series-connected transmit coils 703, 704with an AC signal. Within the first body-implanted device, the chargereceiving system 720 includes a receive coil 721 that is preferablytuned to the resonant frequency of the associated transmit coil 73within the external charging system 700, so that receive coil 721 mayreceive energy transferred from the transmit coil 703 when in closeproximity thereto. The receive coil 721 is coupled to arectifier/de-tune block 722 for receiving energy at times and generatinga rectified output voltage on node 724, and for de-tuning the receivecoil 721 at other times, responsive to a respective BACK TELEM TX DATAsignal on node 725, to inhibit transfer of energy from the transmit coil703. The rectified voltage on node 724 is coupled to power/batterycharging circuitry within the first body-implanted device (not shown).In this embodiment the BACK TELEM TX DATA signal functions as both abit-serial data signal and a “disable charge transfer” signal, much likethe DE-TUNE signal in the previous embodiment. In order to de-tune thereceive coil 721 and disable charging, the BACK TELEM TX DATA signal isdriven and held in one of its two logic levels (e.g., a logic highlevel), while to actually communicate back telemetry data to theexternal charging system 700, the BACK TELEM TX DATA signal is drivenbetween both its logic levels according to the bit serial data. Any ofseveral encoding formats may be used, but NRZ (“non-return-to-zero”)encoding is assumed here.

Within the second body-implanted device, the charge receiving system 730includes a receive coil 731 that is preferably tuned to the resonantfrequency of the associated transmit coil 74 within the externalcharging system 700, so that receive coil 731 may receive energytransferred from the transmit coil 704 when in close proximity thereto.The receive coil 731 is coupled to a rectifier/de-tune block 732 forreceiving energy at times and generating a rectified output voltage onnode 734, and for de-tuning the receive coil 731 at other times,responsive to a respective BACK TELEM TX DATA signal on node 735, toinhibit transfer of energy from the transmit coil 704. The rectifiedvoltage on node 734 is coupled to power/battery charging circuitrywithin the second body-implanted device (not shown).

The external charging system 700 includes circuitry to generate a COILCURRENT signal corresponding to the magnitude of the transmit coilcurrent, and to generate a BACK TELEM RX DATA signal corresponding tothe back telemetry data received from one of the charge receivingsystems 720, 730. The back telemetry data is communicated passively by agiven one of the charge receiving systems 720, 730 by modulating theamount of energy transferred from the external transmit coils andreceived by a given charge receiving system. Such modulation occurs bychanging whether the corresponding receive coil is tuned or de-tuned.De-tuning the receive coil may occur when battery charging (chargetransfer) is complete or not desired, in which case the transferredenergy will decrease and remain at the decreased value, but may alsooccur in response to a bit-serial BACK TELEM TX DATA signal, in whichcase the variations or changes in transferred energy will have afrequency component matching the bit rate of the BACK TELEM TX DATAsignal. The back telemetry data is received by the external chargingsystem by sensing the variation in transmit coil current thatcorresponds to changes in the amount of energy transferred to the givencharge receiving system.

In this embodiment, the circuitry to accomplish this includes a transmitcoil AC current sensor 706 having an input coupled to the output node705 of driver 702, which generates on its output node 707 an AC voltagesignal corresponding to the instantaneous current through theseries-connected transmit coils 703, 704. This AC voltage signal on node77 is coupled to a demodulator 708 which generates on its output node709 a demodulated signal corresponding to the peak value of the ACvoltage signal on node 707, which corresponds to the peak value of theinstantaneous current through the transmit coils 703, 704. Thisdemodulated signal on node 709 is filtered by low-pass filter 710 togenerate the COIL CURRENT signal on node 712. The COIL CURRENT signal isa generally DC-like signal that is reflective of the low-frequencychanges in the peak transmit coil current, such as would occur whencharging is complete (i.e., charge transfer no longer desired) and itscorresponding receive coil is de-tuned and remains de-tuned for sometime.

The demodulated signal on node 709 is also coupled to a band-pass filter711 to generate the BACK TELEM RX DATA signal on node 713. This BACKTELEM RX DATA signal is reflective of higher-frequency changes in thepeak transmit coil current, such as would occur when back telemetry datais being communicated and the corresponding receive coil is de-tuned andtuned responsive to the bit-serial BACK TELEM TX DATA signal.Illustrative waveforms of these signals are shown in FIG. 5B. In someembodiments the data rate for the back telemetry need not be identicalto the data rate for the forward telemetry. For example, the backtelemetry data rate, relative to the resonant frequency of the transmitcoils in the external charging system, may be result in each bitinterval (i.e., bit position) corresponding to as few as 20 cycles ofthe resonant amplifier, as noted in FIG. 5B. Additional examples andother embodiments of such current sensing and receive data circuits aredescribed below.

As noted above, FIG. 5B shows waveforms of selected signals illustratingback telemetry operation in the embodiment shown in FIG. 5A. Inparticular, the bit-serial BACK TELEM TX DATA signal (node 725) is shownrepresenting several bits of information to be communicated from thecharge receiving system 720 to the external charging system 700, alongwith the corresponding tuned or de-tuned status of the receive coil 721.The peak current through the transmit coil 703 is higher correspondingto the de-tuned state of the receive coil 721. A voltage signal isgenerated at the output 707 of the current sensor 706, which voltagesignal corresponds to the instantaneous current through the transmitcoil 73. This output signal 707 is demodulated to produce thedemodulated output signal on node 709, which is then filtered byband-pass filter 711 to produce the BACK TELEM RX DATA signal on node713.

FIG. 6 is a block diagram of an exemplary charging system 745 whichprovides for adjustable transmitted power to improve power efficiencywithin an implanted device. Two charge receiving systems 620, 630 areshown, each disposed within a corresponding body-implanted device, whichare identical to those described in FIG. 2, and need not be describedhere. An external charging system 740 disposed outside a dermis layer602 includes series-connected transmit coils 612, 613, each of whichcorresponds to a respective one of receive coils 621, 631 of respectivecharge receiving systems 620, 630. Two such transmit coils 612, 613 areshown, one for each charge receiving system 620, 630, but otherembodiments may utilize one transmit coil or another number of transmitcoils, depending upon the number of body-implanted devices.

The external charging system 740 includes a resonant driver 743 fordriving the series-connected transmit coils 612, 613 with an AC signal,and a buck/boost circuit 741 that provides on node 742 a variable DCvoltage for use by the driver 743 as an upper power supply node. Byvarying this VBOOST voltage on node 742, the amount of energy storedeach resonant cycle in the transmit coils and ultimately transferred tothe corresponding receive coil may be varied, for example, to achievebetter charging (charge delivery) efficiency and coupling within theimplanted device. The resonant driver 743 is responsive to a CTRLsignal, such as described above regarding other embodiments, which mayfunction as both a data signal and as an enable signal.

The VBOOST voltage on node 742 may be varied as battery chargingprogresses (or the charge delivery requirements change) within eachbody-implanted device. For example, during an early phase of chargingwhen the battery voltage is relatively low, it may be desirable to limitthe rectified voltage on node 624 so that any voltage drop across thecharging circuit within the body-implanted device is kept to a minimumnecessary to achieve proper voltage regulation, or to provide aparticular constant magnitude of battery charging current, toefficiently charge the battery. Later, as battery charging progressesand the battery is charged to a higher voltage, the rectified voltage onnode 624 may be increased to maintain a desired voltage drop across suchcharging circuitry or to maintain the desired battery charging current.When one of the body-implanted devices is fully charged and its receivecoil (e.g., 621) is de-tuned, the other body-implanted device may stillbe charging and its receive coil (e.g., 631) still tuned for resonantenergy transfer from the external charge system. The VBOOST voltage maythen be adjusted to optimize the amount of energy transfer into theremaining body-implanted device.

The buck/boost circuit 741 is shown as being responsive to an ADJUSTCTRL signal, which may be controlled within the external charging systemin response to detecting a decrease in energy transfer to one or morebody-implanted devices (e.g., using the COIL CURRENT signal describedabove), by receiving back telemetry information from one or bothbody-implanted devices regarding internal voltage levels, internalcurrent levels, and/or internal temperatures, or by one or moretemperature sensors within the external charging system (e.g., a sensorplaced near each transmit coil), or by any other useful means, such asinformation from one or both body-implanted devices conveyed using aBluetooth connection to the external charging system. This adjustabilityof the VBOOST voltage provides for adjustable control of the energycoupled to one or both of the charge receiving systems within thebody-implanted devices, even though both series-connected transmit coils612, 613 are driven by a single driver circuit 743. However, it shouldbe noted that changing of the amount of energy that can be coupled toany of the body-implanted devices will change the amount of energytransfer to all the body-implanted devices. Thus, although not disclosedherein, the body-implanted devices must operate such that chargedelivered is governed by the one of the body-implanted devices thatrequires the most charge. Each of the body-implanted devices, forexample, will send information back to the external charging (chargedelivery) system in the form of a request to indicate an increased needfor charge, and the amount of charge transfer will be increased untilthe body-implanted device requiring the most charge has that requestsatisfied.

FIG. 7A is a block diagram of an exemplary system 780 which includesfeedback excitation control of a resonant coil driver amplifier. Twocharge receiving systems 620, 630 are shown, each disposed within acorresponding body-implanted device, which are identical to thosedescribed in FIG. 2, and need not be described here. An externalcharging (charge delivery) system 770 disposed outside a dermis layer602 includes series-connected transmit coils 773, 774, each of whichcorresponds to a respective one of receive coils 621, 631 of respectivecharge receiving systems 620, 630. While two such charging (chargedelivery) coils 773, 774 are shown, one for each charge receiving system620, 630, other embodiments may utilize one transmit coil or anothernumber of transmit coils, depending upon the number of body-implanteddevices.

The external charging system 770 includes a resonant driver 771 fordriving the series-connected transmit coils 773, 774 with an AC signal.An adjustable VBOOST voltage is conveyed on node 742 to provide avariable DC voltage for use by the driver 771 as an upper power supplynode. The resonant driver 771 is responsive to a CTRL signal, such asdescribed above, which may enable/disable the driver 771 whenappropriate (e.g., after battery charging is complete within bothbody-implanted devices), and may also convey forward telemetryinformation to one or both body-implanted devices, both as describedabove. The external charging system 770 also includes a coil currenttrigger circuit 772 for generating on node 776 a TRIGGER signal conveyedto the resonant driver 771 to provide a periodic “excitation” signal toperiodically pump additional energy into the resonant driver 771, whichis helpful to maintain a high degree of efficiency of the resonantoperation of the driver 771 in concert with the series-connectedtransmit coils 773, 774 connected to the output node 775 of the resonantdriver 771. The coil current trigger circuit 772 preferably isconfigured to assert the TRIGGER signal when the instantaneous transmitcoil current, during each resonant cycle, crosses a predeterminedthreshold that is proportional to the peak instantaneous transmit coilcurrent. In other words, when the instantaneous transmit coil currentcrosses a value that is a predetermined percentage of the maximumcurrent (e.g., 60% of peak current), the TRIGGER signal is asserted topump the additional energy into the resonant amplifier (i.e., driver 771and transmit coils 773, 774). Illustrative waveforms of theinstantaneous transmit coil current and the TRIGGER signal are shown inFIG. 7B.

By generating a feedback-controlled TRIGGER signal in this manner, highefficiency resonant operation may be achieved even as the transmit coilcurrent may vary. Such variation in transmit coil current may resultfrom changes in the VBOOST voltage, from changes in transferred energydue to receive coil de-tuning within an associated charge receivingsystem, from forward telemetry which modulates the transmit coil (i.e.,“charging coil”) current, from variations in component parameters, andfrom changes in voltage, temperature, or other environmental conditions.

Headset Charging (Charge Delivery) System

FIG. 8 is a block diagram of an exemplary headset 781 that includes anexternal charging system for two head-located body-implanted devices,such as two implantable pulse generator (IPG) devices. The headsetincludes an IPG Driver and Telemetry block 782 that drives two transmitcoils 783, 784, and which is powered by a battery voltage VBAT conveyedon node 785 by headset battery 788, and an adjustable voltage VBOOSTconveyed on node 786. A buck/boost circuit 787 receives the VBAT voltageon node 785 and generates the VBOOST voltage on node 786. The headsetbattery 788 is charged by a Headset Battery Charger 789 which receivesUSB power from USB port 791. A VDD regulator 790 also receives the VBATvoltage on node 785 and generates a VDD voltage (e.g., regulated to 3.0volts) on node 794, which is generally used as a power supply voltagefor certain circuitry within the headset.

A microcontroller (MCU) 793 provides general configuration control andintelligence for the headset 781, and communicates with the IPG Driverand Telemetry block 782 via a forward telemetry signal FWD TELEM and aback telemetry signal BACK TELEM via a pair of data lines 796. The MCU793 can also communicate with an external device (e.g., a smartphone orpersonal digital assistant (PDA), a controller, a diagnostic tester, aprogrammer) that is connected to the USB port 791 via a pair of USB datalines 792. The MCU 793 is connected to an external crystal resonant tankcircuit 797 for providing an accurate timing source to coordinate itsvarious circuitry and data communication interfaces. A Bluetoothinterface 795 provides wireless interface capability to an externaldevice, such as a smartphone or other host controller, and is connectedto the VDD voltage on node 794. The Bluetooth interface 795 communicateswith the MCU 793 using data/control signals 798. In general, MCU 793 isutilized to store configuration information in an on-chip Flash memoryfor both the overall headset and charging system and also provideconfiguration information that can be transferred to one or more of thebody-implanted devices. The overall operation of the headset is that ofa state machine, wherein the IPG driver/telemetry block 782 and theother surrounding circuitry, such as the buck/boost circuit 787 and theheadset battery charger 789, all function as state machines, typicallyimplemented within an ASIC. Thus, when communication information isreceived that requires the MCU 793 to transfer configuration informationto the body-implanted device or, alternatively, to configure the headsetstate machine, the MCU 793 will be activated. In this embodiment a statemachine is utilized for most functionality because it has lower poweroperation, whereas an instruction-based processor, such as the MCU 793,requires more power. It should be understood, however, that such aheadset can utilize any type of processor, state machine orcombinatorial logic device.

FIG. 9, which includes FIGS. 9A and 9B, is a schematic diagram of anexemplary IPG driver and IPG telemetry circuit, such as the IPG Driverand Telemetry block 782 shown in FIG. 8. While these FIGS. 9A and 9Beach represent a portion of the complete FIG. 9 and may be arrangedabove and below each other (aligned at the dotted line on each figure)to view the entire FIG. 9, the portion shown on FIG. 9A may be generallyreferred to as the IPG driver circuit, even though certain portions ofthe IPG driver circuit is shown in FIG. 9B, and the portion shown onFIG. 9B may be generally referred to as the IPG telemetry circuit, eventhough certain portions of the IPG telemetry circuit is shown in FIG.9A.

Referring now to the complete FIG. 9, a portion of a charging (chargedelivery) system is depicted which includes a coil driver 161 for a pairof series-connected transmit coils 151, 152, and a driver controlcircuit 162 for the coil driver 161. The coil driver 161 together withthe transmit coils 151, 152 may be viewed as a resonant amplifiercircuit 163. The driver control circuit 162 provides a control signal onnode 114 that serves to turn off the coil driver 161 at times, and toperiodically cause energy to be pumped into the resonant amplifier 163at other times, as will be explained below.

The coil driver 161 may be understood by looking first at excitationcoil 144 and driver transistor 133. In resonant operation, the drivertransistor 133 is periodically turned on, which drives the voltage ofnode 134 to ground (labeled 130). Since the excitation coil 144 isconnected between node 786, which conveys a VBOOST voltage, and node134, which is now grounded by transistor 133, the VBOOST voltage isimpressed across the excitation coil 144 and consequently a currentflows through the excitation coil 144, which current stores energy inthe excitation coil 144. The magnitude of the VBOOST voltage may bevaried (e.g., between 1.0 and 5.5 volts) to vary the amount of energystored in the excitation coil 144 per cycle, to thus vary the amount ofenergy coupled to the receive coils (also referred to as “secondarycoils”). Capacitor 145 provides local filtering for the VBOOST voltageconveyed on node 786. When the driver transistor 133 is then turned off,the energy in excitation coil 144 is “pumped” into the LC resonantcircuit formed by parallel-connected capacitors 141, 142, 143 connectedin series with the transmit coils 151, 152. Resistor 153 represents theparasitic resistance of the transmit coils 151, 152 and their associatedwiring. Illustrative waveforms are shown in FIGS. 1A, 10B, and 10C. Incertain embodiments, the resonant frequency is preferably on the orderof 750 kHz.

Three separate capacitors 141, 142, 143 are used to distribute the peakcurrent that would otherwise flow through the leads, solder joints, andstructure of a single capacitor, to instead achieve a lower peak currentthrough each of capacitors 141, 142, 143. But in understanding theoperation of this circuit, these three capacitors 141, 142, 143 may beviewed as effectively providing a single resonant capacitor. When drivertransistor 133 is turned on, it is desirable to drive node 134 to avoltage as close to ground as possible, to reduce losses that wouldotherwise result from a large drain-to-source current and a non-zerodrain-to-source voltage across driver transistor 133. Consequently, thedrain terminal of driver transistor 133 is connected by several distinctpackage pins to node 134.

Driver transistor 133 is controlled by the output 131 of buffer 125,which is coupled to the gate of driver transistor 133 through resistor132. The buffer 125 is connected to operate as an inverting buffer sincethe non-inverting input IN (pin 4) is connected to VCC (pin 6), and theinverting input INB (pin 2) is utilized as the buffer input that isconnected to node 114, which is the control signal generated by drivercontrol circuit 162. Thus, when node 114 is low, the output node 131 ofbuffer 125 is high, and driver transistor 133 is turned on. The outputnode 131 is coupled to the gate of driver transistor 133 throughresistor 132 to limit the peak current charging and discharging the gateterminal of driver transistor 133, and to also provide (together withthe parasitic gate capacitance of driver transistor 133) an RC filterfor the signal actually coupled to the gate terminal of drivertransistor 133.

As mentioned above, when driver transistor 133 is turned on, it isdesirable for node 134 to be driven to a voltage as close to ground aspossible. To help achieve this, it may be likewise desirable to drivethe gate terminal of driver transistor 133 to a voltage higher than thebattery voltage VBAT conveyed on node 785. To accomplish this, a localpower circuit including diodes 127, 129, 136, 137, and capacitors 128,138, may be utilized.

During circuit startup, the buffer circuit 125 operates with its “VCCvoltage” (conveyed on local power node 126) essentially at the batteryvoltage VBAT, less a small diode drop through diode 129. The VBATvoltage may be 3.5-4.0 volts, which is sufficient to operate the buffer125 to provide adequate output voltage levels on node 131 tosufficiently turn on/off driver transistor 133 to initiate and maintainresonant operation. In such resonant operation, driver transistor 133 ispreferably turned off at a particular time in each resonant cycle topump energy into the resonant circuit, as will be explained furtherbelow. Each time that the driver transistor 133 is turned off, thevoltage on node 134 rises quickly as the current through excitation coil144 continues to flow into node 134 and charges capacitor 135. Thisrising voltage is coupled through capacitor 138 onto node 139, throughdiode 136, and onto the local power node 126 for buffer 125. Themagnitude of the positive-transition of the voltage on node 134 resultsin a voltage on local power node 126 that may be as high as 8.0 volts,which is higher than the VBAT voltage, especially when operating in thelower range of battery voltage (e.g., as the battery discharges). Whenthe voltage of local power node 126 rises above the VBAT voltage, diode129 prevents any back-current into the VBAT node 785, and Zener diode127 operates to limit, for safety reasons, the maximum voltage developedon local power node 126. Capacitor 128 provides local filtering on thelocal power node 126 irrespective of whether the buffer 125 is poweredby the battery (through diode 129) or by resonant operation of the coildriver circuit 161 (through diode 136).

The driver control circuit 162 generates on output node 114 a drivercontrol signal that controls when driver transistor 133 is turnedon/off. In resonant operation, the driver control signal 114 ispreferably a periodic signal that causes the driver transistor 133 toturn off at a predetermined time during each resonant cycle, and to turnback on at a later time during each resonant cycle, to thereby causeenergy to be pumped into the resonant amplifier 163 during each resonantcycle. In addition, at certain times the driver control signal 114 ispreferably driven high to cause the driver transistor 133 to turn offand remain off for a time duration longer than a resonant cycle, whichprevents energy from being pumped into the resonant amplifier, and thusallows the resonant amplifier operation to decay and eventually cease.

The driver control circuit 162 includes a Schmitt-trigger NAND gate 18having a local power supply node 112 (also labeled 4VF) which is coupledto the battery voltage VBAT using a small noise-isolation resistor 120and a local filter capacitor 113. An input circuit includes capacitor107, diode 110, and resistor 111, which together generate a first inputsignal on node 109 (NAND input pin 2) responsive to a TRIGGER signalconveyed on node 106. A feedback circuit includes diode 122, resistors118, 119, and capacitor 105, which together generate a second inputsignal on node 104 (NAND input pin 1) responsive to the driver controlsignal generated on the output node 114.

To understand operation of the driver control circuit 162 during normaloperation of the resonant amplifier circuit 163, assume that the TRIGGERsignal 106 is high, both inputs of NAND 108 (nodes 104, 109) are high,and the output of NAND 108 (driver control signal 114) is low.Consequently, node 131 is high (due to inverting buffer 125) and drivertransistor 133 is turned on, driving node 134 to ground and causingcurrent to flow from VBOOST (node 786) through the excitation coil 144to ground.

As will be explained in detail below, the TRIGGER signal on node 106 isthen driven low, thus creating a falling-edge (i.e., negativetransition) on the voltage of node 106. Capacitor 107 couples thisnegative transition to node 109, which is coupled to a voltage below thelower input threshold of Schmitt NAND gate 108. As a result, the outputnode 114 is driven high, node 131 is driven low, and transistor 133 isturned off. This happens almost immediately after the falling edge ofthe TRIGGER signal 106.

With the TRIGGER signal 106 still low, the resistor 111 will charge node109 until its voltage reaches the upper input threshold of Schmitt NANDgate 18, at which time the NAND gate 108 output node 114 is again drivenback low, node 131 is driven high, and transistor 133 is turned on. Thevalues of resistor 111 and capacitor 107 are chosen, in concert with theupper and lower input thresholds of the Schmitt NAND gate 108, todetermine the output high pulse width of output node 114, and thusdetermine the length of time that transistor 133 is turned off.

When the TRIGGER signal 106 is driven back high, this positivetransition is coupled by capacitor 107 to node 109, but the coupledcharge is snubbed by diode 110 to prevent an excessive positive voltagethat would otherwise be generated at node 109, and instead maintain thevoltage of node 109 at essentially the VBAT voltage.

If there are no transitions of the TRIGGER signal 106, the voltage ofnode 109 (NAND input pin 2) remains high, and the feedback circuit(diode 122, resistors 118, 119, and capacitor 105) causes the outputnode 114 to oscillate. This occurs because the voltage of node 104 (NANDinput pin 1) slowly follows the voltage of the output node 114 due tothe RC circuit formed by the feedback resistors 118, 119 (and diode 122)coupled between the output node 114 and input node 104, and thecapacitor 105 coupled to node 104 itself. Diode 122 is included so thatthe parallel combination of resistors 118, 119 charges node 104 after apositive-going output transition, while only resistor 119 dischargesnode 104 after a negative-going output transition. This asymmetry helpskeep node 104 nominally very close to the VBAT level during normalresonant operation, to essentially disable the “watchdog timer” aspectof this circuit as long as periodic TRIGGER signals are received.

The component values of resistors 118, 119 and capacitor 15 arepreferably chosen so that the self-oscillation frequency of node 114 ismuch lower than the resonant frequency of operation (and likewise theexpected frequency of the TRIGGER signal 106 during resonant operation,as will be explained in greater detail below). In some embodiments theself-oscillation frequency is approximately 3-4 times lower than theresonant frequency. This self-oscillation provides a suitable periodicconduction path through driver transistor 133 to initiate operation ofthe resonant amplifier 163 until the TRIGGER signal 106 is generated percycle, which provides for more efficient operation and greater spectralpurity of the resonant amplifier circuit 163. Resistors 116 and resistor117 form a voltage divider to generate on node 115 an IPG_CHRG_FREQsignal reflective of the actual charger frequency

A forward telemetry data signal FWDTELEM conveyed on node 101 is coupledto the gate terminal of NMOS transistor 103, which terminal is coupledto ground 130 by biasing resistor 102. The operation described thus-farabove assumes that the FWDTELEM signal remains at ground, and thustransistor 103 remains turned off. If the FWDTELEM signal is drivenhigh, NAND gate 108 input node 104 is driven to ground, which causes theNAND gate 108 output node 114 to be driven high, irrespective of thesecond NAND input node 109. This, of course, turns off driver transistor133 for as long a time as FWDTELEM remains high, and causes resonantoperation of the resonant amplifier circuit 163 to decay and eventually,if disabled for a long enough time, to cease entirely. Then, when theFWDTELEM signal is driven back low and transistor 103 turns off, thedriver control circuit 162 begins to self-oscillate, thus startingoperation of the resonant amplifier circuit 163 and the eventualgeneration of the TRIGGER signal 16 to more precisely control the timingof driver transistor 133. Such resonant “lock-in” occurs fairly quickly,usually in only 1-2 cycles. In some embodiments, the resonant frequencyis approximately 750 kHz, and the forward data rate is approximately 10kHz (i.e., a 100 μS bit interval), and the time required for theresonant amplifier 163 to decay (when FWDTELEM is driven high), and tore-start and lock-in resonant operation (when FWDTELEM is driven low),is a small portion of an individual bit interval. A more detaileddescription of such forward data transmission, including receiving suchtransmitted data in a charge receiving system, follows below.

As described above, in normal resonant operation the negative transitionof the TRIGGER signal 106 determines when the driver transistor 133 isturned off during each resonant cycle of the amplifier circuit 163, andthe RC input circuit on node 109 determines how long the drivertransistor 133 remains off. Preferably the driver transistor 133 has a3% duty cycle (i.e., turned off 30% of the time). In thisimplementation, feedback circuitry shown in FIG. 9B is utilized thatgenerally tracks the actual current through the transmit coils 151, 153,and generates the negative-going transition of the TRIGGER signal 106 ata time during each resonant cycle when the increasing instantaneoustransmit coil current exceeds a predetermined percentage of the peakcurrent through the transmit coils 151, 152. Careful selection of thepredetermined percentage improves the efficiency of resonant amplifieroperation and reduces unwanted harmonic components of the oscillationfrequency.

The generation of the TRIGGER signal 106 begins with acurrent-to-voltage converter circuit 260 formed by the series-connectedresistors 203, 204 and capacitor 206 coupled between the HV node 140(the same node driving the series-connected transmit coils 151, 152) andground 130. Resistor 205 is a biasing resistor. With proper selection ofcomponent values, the instantaneous voltage generated at node 202 willbe proportional to the instantaneous current through the transmit coils151, 152. Such may be achieved by proper selection of the resistor andcapacitor values in the current-to-voltage converter circuit 260 toachieve the same time constant as the inductor and parasitic resistorvalues in the transmit coils. Specifically, the values are preferablychosen so that R/C=L/R. Referencing the actual components, thisrelationship is then (R₂₀₃'R₂₀₄)/C₂₀₆=(L₁₅₁'L₁₅₂)/Rp₁₅₃ (e.g., whereR₂₀₃ means the value of resistor 203). If this relationship is followed,the instantaneous voltage at node 202 is an AC voltage that isproportional to (i.e., corresponds to) the instantaneous AC currentthrough the transmit coils 151, 152. Normally, this AC voltage on node202 would be symmetric and centered around the ground voltage, as shownin FIG. 1A, but in this embodiment the AC voltage on node 202 is offsetto a non-negative voltage range by a ground restore circuit 261.

The ground restore circuit 261 includes an amplifier 207 having a localpower supply node 21 (also labeled 4VH) which is coupled to the batteryvoltage VBAT (conveyed on node 785) using a small noise-isolationresistor 209 and a local filter capacitor 208. The amplifier 207non-inverting input (pin 3) is coupled to ground, and the invertinginput (pin 2) is coupled to node 202. A feedback circuit includescapacitor 210, resistor 211, and diode 212. In operation, this groundrestore circuit 261 translates the AC voltage signal on node 202 to anon-negative voltage signal of the same magnitude, whose peak lowvoltage is ground, and whose peak high voltage is twice that otherwisegenerated on node 202 in the absence of the ground restore circuit 261.This resulting waveform for node 202 is shown in FIG. 10A. The peakvoltage at node 202 may be 2-3 V.

The signal on node 202 is coupled to a demodulator circuit 262 thatincludes amplifier 213, diode 215, resistors 217, 219, and capacitors218, 220. Node 202 is coupled to the non-inverting input (pin 5) ofamplifier 213. The inverting input (pin 6) of amplifier 213 is coupledto the output node 214 to achieve operation as a voltage follower. Diode215 and capacitor 218 generate on node 216 a voltage corresponding tothe peak voltage driven onto node 214 by amplifier 213 (less a smallvoltage drop through diode 215), and bleeder resistor 217 reduces thevoltage on node 216 if the peak voltage on node 214 assumes a lowervalue corresponding to a decrease in the current through the transmitcoils 151, 152. Such a situation will be more fully described below inthe context of back telemetry. Lastly, the peak voltage on node 216 isRC-filtered by resistor 219 and capacitor 220 to generate on node 257 asignal having less ripple than the signal on node 216. This signal onnode 257 is then buffered by the buffer 263 which includes an amplifier221 (also configured as a voltage follower) to generate on node 222 amore robust signal representing the magnitude of the peak currentthrough the transmit coils 151, 152. Resistors 230, 233 and filtercapacitor 231 generate a TELEM_CURRENT signal on node 232 having ascaled magnitude relative to the peak transmit coil current representedby node 222. In this implementation, with preferred values of theresistors 230, 233, the TELEM_CURRENT signal has a magnitude that isone-half the magnitude of the peak transmit coil current.

Comparator 228 is configured to essentially “compare” the instantaneoustransmit coil current against a percentage of the peak transmit coilcurrent, and generate the falling-edge on the TRIGGER signal 106 duringeach cycle of resonant operation when the rising edge of theinstantaneous transmit coil current rises above a predeterminedpercentage of the peak transmit coil current.

The voltage signal on node 202 corresponds to the instantaneous transmitcoil current, which is coupled through resistor 227 to the invertinginput of comparator 228. The peak transmit coil current signal on node222 is divided by a resistor divider formed by resistors 225, 223 togenerate on node 226 a reference signal representing a predeterminedpercentage of the peak transmit coil current. Capacitor 224 provideslocal filtering to stabilize this signal on node 226, which is coupledto the non-inverting input of comparator 228. When the inverting inputof comparator 228 rises above the non-inverting input, the output signalTRIGGER on node 16 is driven low, as is depicted in FIG. 10A.

The “peak transmit coil current” signal on node 222 varies as one ormore secondary coils is de-tuned, such as would occur to indicate thatcharging is complete (if such de-tuning occurs continuously) or tocommunicate back telemetry data from one of the body-implanted devices(if such de-tuning is performed corresponding to a bit-serial datastream). The TELEM_CURRENT signal on node 232 is preferably configuredto correspond to slowly changing values of the peak transmit coilcurrent, while the remaining circuitry to the right of amplifier 221 isutilized to detect more frequent (i.e., higher frequency) changes in thetransmit coil current, as would occur during back telemetry of data fromone of the body-implanted devices.

The buffer 263 output signal on node 222 is AC-coupled through capacitor234 to node 246, which is nominally biased by resistors 235, 236 atone-half the 4VH voltage on node 201, which essentially is the VBATvoltage on node 785. Thus, node 246 has a nominal DC bias equal toVBAT/2, upon which is superimposed an AC signal corresponding to changesin the magnitude of the peak transmit coil current. This node 246 iscoupled to an input of a band-pass filter/amplifier 264, which includesan amplifier 237, resistors 239, 241 and capacitors 240, 248.Specifically, node 246 is coupled to the non-inverting input ofamplifier 237. Feedback resistor 239 and capacitor 240 are each coupledbetween the output node 238 of amplifier 237 and the inverting inputnode 247 of amplifier 237.

The band-pass filter/amplifier 264 generates on its output node 238 ananalog signal representing received data. This analog data signal iscoupled through resistor 242 to generate an analog “back telemetry”signal BKTELEM_ANA. The band-pass filter/amplifier 264 also generates onnode 245 a reference signal corresponding generally to the mid-point ofthe transitions of the analog data signal on node 238, which is the samebias level (e.g., VBAT/2) as node 246. This signal is coupled throughresistor 256 to generate a reference “back telemetry” signalBKTELEM_REF. Both the BKTELEM_ANA and BKTELEM_REF signals may beconveyed to control circuitry (not shown) and may be used as diagnostictest points.

The gain of the band-pass filter/amplifier 264 is determined by thevalue of resistor 239 divided by the value of resistor 241. In certainpreferred implementations, the gain may be equal to 10. The value ofcapacitor 240 is selected to provide the desired high frequency rolloff,and the value of capacitor 248 is selected to provide the desired lowfrequency rolloff.

The analog data signal on node 238 and the analog reference signal onnode 245 are coupled to a comparator circuit 265 to generate on itsoutput node 250 a digital signal representing the back telemetry datasignal. The comparator circuit 265 includes a comparator 249 having alocal (4VG) power supply node 254 which is coupled to the batteryvoltage VBAT (conveyed on node 785) using a small noise-isolationresistor 253 and a local filter capacitor 255. In this implementation,the comparator circuit 265 is preferably configured to provide a voltagegain of 27, which is determined by the input resistor 243 connectedbetween node 238 (i.e., the output node of the band-passfilter/amplifier circuit 264) and the non-inverting input node 244 ofcomparator 249, and the feedback resistor 252 connected between theoutput node 250 of comparator 249 and the non-inverting input node 244of comparator 249. The voltage of this non-inverting input node 244 iscompared to the data reference voltage coupled to the inverting inputnode 245 of comparator 249 to generate on output node 250 the digitalsignal representing the back telemetry data signal. This digital signalis coupled through resistor 258 to generate on node 251 a digital backtelemetry data signal BKTELEM_DIG.

FIG. 11 is a schematic diagram of an exemplary headset buck/boostcircuit, such as the buck/boost circuit 787 shown in FIG. 8. In thisembodiment, the buck/boost circuit utilizes a commercially availablehigh efficiency single-inductor buck-boost converter circuit 369, suchas the TPS63020 from Texas Instruments, Inc. The VBAT voltage conveyedon node 785 is coupled to an input filter circuit that includescapacitor 351, ferrite bead 352, and capacitors 354, 355, whose outputon node 353 is coupled to a pair of voltage input pins VIN1, VIN2 of theconverter circuit 369. A single inductor 371 is coupled between a firstpair of connection pins L1, L2 (node 37) and a second pair of connectionpins L3, L4 (node 372). The output of the converter circuit 369 isprovided on a pair of output pins VOUT1, VOUT2, which are coupled vianode 367 to an output filter circuit that includes capacitors 374, 375,376 and ferrite bead 380, to provide the VBOOST voltage on node 786. Aprecision resistor divider 377, 378 provides a monitoring voltageBOOST_MON on node 379.

A boost enable input signal BOOST_EN is coupled via node 359 to anenable input EN of the converter circuit 369, and also coupled to anRC-filter circuit formed by resistor 357 and capacitor 356, whose outputon node 358 is coupled to a VINA pin (supply voltage for the controlstage) and SYNC pin (enable/disable power save mode; clock signal forsynchronization) of the converter circuit 369. The converter outputvoltage on node 366 is coupled to a voltage divider circuit thatincludes resistors 373, 365 to generate on node 366 a feedback voltagewhich is coupled to the FB input of the converter circuit 369. A boostPC input signal BOOST_PC is coupled via node 360 to a voltage divideradjustment circuit that includes resistors 361, 363 and capacitor 364,each coupled to node 362, and whose output is coupled to node 366. Inthis manner the BOOST_PC signal can essentially alter the voltagedivider ratio to adjust the output voltage of the converter 369 and thusalter the VBOOST voltage.

As noted above, FIGS. 10A, 10B, and 10C illustrate voltage waveforms ofselected signals depicted in the embodiment shown in FIG. 9, and alsoseveral signals depicted in FIG. 13A. FIG. 10A generally illustrateswaveforms related to sensing the transmit coil current and generatingthe TRIGGER signal accordingly. The various waveforms show the transmitcoil current, the I-to-V Converter 260 output signal on node 202 withoutthe effect of the ground restore circuit 261, the I-to-V Converter 260output signal on node 202 with the effect of the ground restore circuit261, the demodulator node 257, the reference node 226 (shown having avalue equal to 60% of the peak voltage on node 257), and the resultingTRIGGER signal on node 106. The left half of the figure corresponds to alower magnitude of transmit coil current, and the right half of thefigure corresponds to a higher magnitude of transmit coil current.

FIG. 10B generally illustrates waveforms related to the driver control162 and the resonant amplifier 163. Shown are the TRIGGER signal on node106, the resulting waveform on NAND 108 input 2 (node 109), the NAND 108input 1 (node 104), the resulting waveforms on the NAND 108 output node114, and the buffer 125 output node 131, the resulting voltage on thedrain terminal of transistor 133 (node 134), and the current through thetransmit coils 151, 152. The resonant oscillation frequency in thisexemplary embodiment corresponds to an oscillation period of about 1.33microseconds.

FIG. 10C generally illustrates waveforms related to forward telemetryoperation. The upper waveform illustrates the FWDTELEM signal on node101 conveying a serial bit stream data signal conveying several bits ofinformation, with each bit interval, for this exemplary embodiment,being about 100 microseconds long. When the FWDTELEM signal is drivenhigh at transition 322, the NAND 18 input 1 (node 104) is driven toground, as shown in the second waveform, to disable the transmit coildriver 161. As a result, the previously oscillating signal on the gatenode 131 of transistor 133 is likewise driven to ground, as shown in thethird waveform, which disables the resonant amplifier 163 and causes thetransmit coil 151, 152 current to decay and eventually cease, as shownin the fourth waveform. The fifth and sixth waveforms are describedbelow in detail with regard to FIG. 13A, and illustrate the current inthe receive coil 402 likewise decays and ceases, resulting in acorresponding signal on the negative peak detector output node 410, anda resulting falling transition 323 on the FWD TELEM RX DATA signal onnode 419. An additional logical inversion of this signal may be easilyaccomplished to generate a data signal having the same polarity as theFWDTELEM signal on node 101.

When the FWDTELEM signal is driven low at transition 324, the NAND 108input 1 (node 104) charges back to a high level, which allows the drivercontrol 162 to again oscillate, initially controlled by its own feedback“watchdog timer” operation, and later under control of the TRIGGERsignal. As a result, the gate node 131 of transistor 133 again exhibitsan oscillating signal causing transistor 133 to periodically “pump” theresonant amplifier 163, and the transmit coil 151, 152 once againoscillates, as shown in the fourth waveform. As described below indetail with regard to FIG. 13A, the current in the receive coil 402 isinduced because of the transmit coil current, resulting in acorresponding signal on the negative peak detector output node 410, anda resulting rising transition 325 on the FWD TELEM RX DATA signal onnode 419.

Implantable Pulse Generator

FIG. 12 is a block diagram of an exemplary body-implantable activedevice 400, such as an implantable pulse generator (IPG) device. Areceive coil 402 (also referred to as a secondary coil 402) is connectedto a RECTIFIER block 401 that generates a PWRIN signal on node 408 andan RFIN signal on node 414. Both the PWRIN signal on node 408 and theRFIN signal on node 414 are connected to a TELEMETRY/DE-TUNE block 451that receives a forward telemetry signal on the RFIN node 414, and whichinteracts with the PWRIN node 408 to de-tune the receive coil 402 tothereby communicate back telemetry information and/or disable furtherenergy transfer to the receive coil 402. The PWRIN node 408 is alsoconnected to a POWER/CHARGER block 453 that is responsible forgenerating one or more internal voltages for circuitry of thebody-implantable device 400, and for charging battery 459.

A microcontroller (MCU) 457 provides overall configuration andcommunication functionality and communicates forward and back telemetryinformation via a pair of data lines 419, 425 coupled to the TELEMETRYblock 451. Data line 419 conveys a forward telemetry RX signal, and dataline 425 conveys a back telemetry TX signal. The MCU 457 receivesinformation from and provides configuration information to/from thePOWER/CHARGER block 453 via control signals PWR CTRL conveyed on controllines 452. A programmable electrode control and driver block 454(DRIVERS 454) generates electrical stimulation signals on each of agroup of individual electrodes 455. An adjustable voltage generatorcircuit BOOST 458, which is coupled via signals VSUPPLY (node 430), SW(node 433), and VBOOST DRV (node 438) to components external to the ASIC450 (including capacitor 431, inductor 432, and rectifier block 437)provides a power supply voltage VSTIM to the DRIVERS block 454.

The MCU 457 provides configuration information to the DRIVERS block 454via configuration signals CONFIGURATION DATA conveyed on configurationlines 456. In some embodiments, the POWER/CHARGER block 453, theTELEMETRY block 451, the BOOST circuit 458, and the DRIVERS block 454are all implemented in a single application specific integrated circuit(ASIC) 45, although such is not required. In the overall operation, theASIC 45 functions as a state machine that operates independently of theMCU 457. The MCU 457 includes Flash memory for storing configurationdata from the external control system (not shown) to allow a user todownload configuration data to the MCU 457. The MCU 457 then transfersthis configuration data to ASIC 45 in order to configure the statemachine therein. In this manner, the MCU 457 does not have to operate togenerate the driving signals on the electrodes 455. This reduces thepower requirements. Other embodiments may implement these threefunctional blocks using a combination of multiple ASIC's, off-the-shelfintegrated circuits, and discrete components.

Battery charging (charge delivery) is monitored by the ASIC 450 andadjusted to provide the most efficient charging (charge delivery)conditions and limit unnecessary power dissipation. Preferableconditions for charging the battery include a charging voltage ofapproximately 4.5 V for most efficient energy transfer (with a minimumcharging voltage of about 4.0 V). Also, it is particularly desirable tomaintain a constant charging current into the battery in a batterycharging operation during the entire charging time, even as the batteryvoltage increases as it charges. Preferably this constant chargingcurrent is about C/2, which means a charging current that is one-halfthe value of the theoretical current draw under which the battery woulddeliver its nominal rated capacity in one hour. To accomplish this, avariety of sensors and monitors (not shown) may be included within thebody-implantable device 400 to measure power levels, voltages (includingthe battery voltage itself), charging current, and one or more internaltemperatures.

FIG. 13A is a schematic diagram of an exemplary RECTIFIER block 41 andTELEMETRY/DE-TUNE block 451, both such as those shown in FIG. 12. Theexemplary RECTIFIER block 41 includes a resonant half-wave rectifiercircuit 421 and a half-wave data rectifier circuit 422. The resonanthalf-wave rectifier circuit 421 may be viewed as an “energy receivingcircuit” and the half-wave data rectifier circuit 422 may be viewed as a“data receiving circuit.” The exemplary TELEMETRY/DE-TUNE block 451includes a current mirror circuit 420, and a de-tuning transistor 424.

The circuitry depicted in FIG. 13A may be viewed as a portion of acharge receiving system which includes a secondary coil 402, an energyreceiving circuit (421), and a data receiving circuit (422). Theresonant rectifier circuit 421 includes diode 405, capacitor 404, andcapacitor 407, which together with the secondary coil 402, operates as aresonant half-wave rectifier circuit. When the secondary coil 402 isdisposed in proximity to its associated transmit coil, such as one ofthe transmit coils 151, 152 (see FIG. 9), during a time when theresonant amplifier 163 is operating, the transmit coil and the secondarycoil may be inductively coupled and may have, with careful design of thecoils and reasonably close physical proximity, a Q that approaches 100.Consequently, the resonant amplifier circuit 163 and the resonantrectifier circuit 421 will operate as a resonant Class E DC-to-DCvoltage converter. During such operation, energy is coupled to thesecondary coil 402 due to magnetic induction.

This induced energy in secondary coil 402 is manifested as a sinusoidalvoltage on node 403 that traverses above and below the ground referencelevel on node 440. This AC voltage on node 403 is half-wave rectified toprovide a DC voltage on node 408 that may be used to provide power toboth operate and/or to charge the battery (if present) within thebody-implanted device. Specifically, because a single diode 405 is usedin this circuit, and due to the polarity of this diode, only thepositive voltage transitions on node 403 are rectified, thus creating apositive DC voltage on node 408. A zener diode 406 is coupled betweennode 408 and ground to prevent an excessive positive voltage from beinggenerated at node 408.

The above description of the resonant rectifier circuit 421 and itshalf-wave rectifier circuit operation has assumed that transistor 424remains off. This ensures that the Q of the combined primary transmitcoil 151 and the secondary coil 402 remains high, and energy isefficiently transferred. However, if transistor 424 is turned on (whenthe DE-TUNE/BACK TX DATA signal on node 425 is high), the secondary coil402 is “de-tuned” which significantly reduces the Q of the resonantcircuit, and thereby reduces charge transfer and thus reduces coupledpower into the secondary coil 402. This may be useful at times to reducepower, such as when the battery has been fully charged or when no chargedelivery is required. It is also useful to turn on transistor 424 tocommunicate back telemetry information to the charging system. Analogousback telemetry operation is described above in reference to FIGS. 5A and9, and corresponding waveforms are shown in FIGS. 5B and 10A.

The data receiving circuit 422 includes diode 409, capacitor 411, andresistor 412, which together may be viewed as a negative half-waverectifier circuit or negative peak-detector circuit. Irrespective ofwhether the de-tune transistor 424 is active, the generated voltage onnode 410 corresponds to the peak negative voltage of the sinusoidalvoltage signal on node 403. If the peak negative voltage increases inmagnitude (i.e., becomes more negative) over multiple cycles, the diode409 will quickly drive node 410 to a correspondingly more negativevoltage, and capacitor 411 serves to maintain this voltage. Conversely,if the peak negative voltage decreases in magnitude (i.e., becomes lessnegative) over multiple cycles, the resistor 412 will drive node 410 toa correspondingly less negative voltage. The value of resistor 412 andcapacitor 411 may be chosen to provide a response time that isconsistent with forward telemetry data rates. Exemplary forwardtelemetry data rates may be on the order of 10 kHz.

The data receiving circuit 422 together with the current mirror circuit420 generates on node 419 a signal FWD TELEM RX DATA reflecting theforward telemetry received data. The current mirror 420 is powered by aVDD voltage conveyed on node 417, and generates a reference currentthrough resistor 413 and P-channel transistor 415, which is mirrored byP-channel transistor 416 to generate a current through resistor 418which generates a corresponding voltage signal on node 419. Dependingupon the current gain of the current mirror 420, node 419 may be eitherdriven virtually all the way to the VDD voltage (less a V_(DSSAT)voltage of transistor 416), or may be pulled by resistor 418 well towardground, to generate a “quasi-digital” forward telemetry receive datasignal. Additional digital regeneration circuitry (e.g., within theASIC, and not shown) may be employed to create a truly digital datasignal.

FIG. 13B generally illustrates voltage waveforms of selected signalsdepicted in the embodiment shown in FIG. 13A. In particular, waveformsare shown for the induced voltage at node 43 (one end of the receivecoil 402), the DE-TUNE gate signal on node 425, the PWRIN signal on node408, the negative peak detector signal on node 410, and the currentmirror output node 419. The left portion 471 corresponds to the receivecoil 402 being “tuned” to transfer charge, the right portion 472corresponds to the receive coil 402 being “de-tuned” to inhibit chargetransfer, in response to the transition 473 of the DE-TUNE gate signalto a high level, as shown in the second waveform. This high voltagelevel turns on transistor 424, which grounds node PWRIN, as shown in thethird waveform, and likewise “clamps” the voltage on node 403 to a smallpositive voltage 474 due to diode 405, while not affecting the negativeinduced voltage 475 on node 403, and similarly without affecting thenegative peak detector voltage on node 410 and the voltage on currentmirror output node 419.

The rightmost portion 476 of the figure shows the induced voltage inreceive coil decaying when the resonant amplifier in the externalcharging system is disabled. This could occur because the externalcharging system turned off its resonant amplifier in response todetecting a long term de-tuning of the receive coil in thebody-implantable active device (i.e., when charge transfer is no longerdesired). This could also occur in response to a back telemetrycommunication calling for charge transfer to cease. This could alsooccur merely because another bit of forward telemetry information iscommunicated. In any of such possible situations, the resonant amplifier163 is disabled, which allows the resonant operation (and AC currentthrough the transmit coils) to decay, and as a result the inducednegative voltage at node 403 of the receive coil likewise decays, asshown by waveforms 477. This causes a corresponding decay in the voltageof negative peak detector node 410, and an eventual change of state 478of the current mirror output node 419.

FIG. 14 is a schematic diagram of portions of an adjustable voltagegenerator circuit, such as the adjustable voltage generator circuitBOOST 458 shown in FIG. 13, and particularly highlights the externalcomponents to the ASIC 450, in accordance with some embodiments of theinvention. In this embodiment, a VSUPPLY voltage generated within theASIC 450 and conveyed on node 430 is coupled to filter capacitor 431 andinductor 432. The other end of the inductor 432 is coupled via node 433to the drain terminal of switch transistor 439 within the ASIC 450,which is controlled by a BOOST CTRL signal connected to its gateterminal. A pair of diodes 434, 435 and capacitor 436 together form arectifier block 437 and serve to rectify the SW signal voltage on node433 and thus generate the VBOOST DRV voltage on output node 438.

FIG. 15 is a diagram representing a headset 580 that includes anexternal charging system 581 for two separate body-implantable devices,each implanted behind a patient's respective left and right ears. Eachof the body-implantable devices may be a head-located neurostimulatorsystem, such as that described below. The charging system 581 isconnected to a pair of headset coils 582, 592 by respective wire pairs583, 593. When the headset 580 is worn by a patient, the headset coils582, 592 (transmit coils) are placed in proximity to the correspondingreceive coil 584, 594 in each respective body-implanted device.

The exemplary headset 580 includes an IPG driver, telemetry circuitry, amicrocontroller (MCU), a battery, and a Bluetooth wireless interface.The headset 580 may also communicate with a smartphone or PDA 596, formonitoring and/or programming operation of the two head-locatedneurostimulator systems.

Full Head-Located Neurostimulator System

FIG. 16 depicts a side view of a head-located, unibody neurostimulatorsystem 40 for migraine and other head pain, which includes animplantable pulse generator (IPG) 10 and two unibody plastic leadextensions—a Frontal-Parietal Lead (FPL) 20 and an Occipital Lead (OL)30 of adequate length to extend to roughly the midline of the foreheadand to the midline at the cervico-cranial junction, respectively. Eachlead includes a plurality of electrodes in a distribution and over alength to allow full unilateral coverage of the frontal, parietal, andoccipital portions of the head. The system 40 may include a unibodyconstruction to provide physical and functional continuity of therelated components and sub-components.

The FPL 20, as part of the unibody construction, extends from the IPG10. The FPL 20 comprises a plastic body member 20 a and a set ofinternal conducting wires 29. The lead internal wires 29 pass along theinterior of the plastic body member 20 a. The plastic body member 20 ais an elongated, cylindrical, flexible member, which may be formed of amedical grade plastic polymer. It has a proximal end 22, a distal end21, and may be conceptually divided into five segments along its lineardimension. Progressing from the proximal end 22, these segmentssequentially include a proximal lead segment (PLS) 22 a, a parietalelectrode array (PEA) 26, an inter-array interval 27, a frontalelectrode array (FEA) 25, and a distal non-stimulating tip 23.

The FEA 25 consists of a plurality of surface metal electrodes (SME) 24uniformly disposed over a portion of the distal aspect of the FPL 2.Lead internal wires 29 connect to the SME 24 as depicted in FIG. 17,which represents the distal four SME 24 of the lead.

Returning to FIG. 16, the PEA 26 consists of a plurality of SME 24uniformly disposed along a linear portion of the FPL 20. The PEA 26 isseparated along the FPL 20 from the FEA 25 by an inter-array interval27. It is separated from the IPG by the PLS 22 a. The lead internalwires 29 connect to the individual SME 24 of the PEA 26 in the samefashion as they do with the SME 24 of the FEA 25.

The occipital lead (OL) 30, as part of the unibody construction, extendsfrom the IPG 10. It comprises a plastic body member 39 and a set of leadinternal wires 38 that pass through the central cylinder of the lead toconnect to a series of SME 34 that are uniformly disposed along aportion of the length of the lead. These lead internal wires 38 pass andconnect in the same manner as described above for the SME 24 of the FEA25 as depicted in FIG. 17.

The plastic body member 39 is an elongated, cylindrical, flexiblemember, which may be formed of a medical grade plastic polymer. It has aproximal end 32 and a distal end 31. Progressing along the lead from theproximal end 32, these segments sequentially include a proximal leadsegment (PLS) 32 a, an occipital electrode array (OEA) 35, and a distalnon-stimulating tip 33.

The OEA 35 consists of a plurality of surface metal electrodes (SME) 34uniformly disposed over a portion of OL 30. Lead internal wires 38connect to the SME 34 in the same fashion as depicted for the FEA asshown in FIG. 17.

Referring to FIG. 16 and FIG. 18, the three primary physical andfunctional components of the IPG 10 include a rechargeable battery 12,an antenna (receive coil) 11, and an application specific integratedcircuit (ASIC) 13, along with the necessary internal wire connectionsamongst these related components, as well as to the incoming leadinternal wires 29, 38. These individual components may be encased in acan made of a medical-grade metal and plastic cover 14, which itselftransitions over the exiting FPL 20 and OL 30.

FIG. 19 depicts a lateral view of the head-located, unibodyneurostimulator system 40 in-situ. The unit is demonstrated in animplant position where the IPG 10 is posterior and cephalad to the pinnaof the ear. The drawings demonstrate the FPL 20 passing over theparietal 60 and frontal 70 regions of the head in a manner that placesthe FEA 25 over the supraorbital nerve 71 and the PEA 26 over theauriculo-temporal nerve 61. The OL 30 is shown passing caudally andmedially over the occipital region 50 of the head such that the OEA 35crosses over the occipital nerve 51. Prominent here is the PEA 26, as itcovers a portion of the parietal region 60 and the major associatednerves, including the auriculo-temporal nerve 61, as well as adjacentcutaneous nerves. Also depicted are the courses of the distal portion ofthe FPL 20 and the OL 30 as they pass over and cover the associatednerves of the frontal (supraorbital) region 70 and occipital region 50.

The overall mechanistic purpose of an implantable neurostimulationsystem is to generate and conduct a prescribed electrical pulse wavefrom an IPG 10 down a set of lead internal wires 29, 38 running aportion of the length of the lead to specified programmed set of SME 24,34, whereby the current is then conducted by tissue and/or fluid to anadjacent, or nearby, set of one or more SME 24, 34, which in turn passesthe signal proximally down the lead wire 29, 38 back to the IPG 10 andits ASIC 13, thus completing the circuit.

In certain embodiments, a body-implantable active device includes ahead-located, unibody neurostimulating system comprising an IPG 10 andat least two neurostimulating leads (e.g., FPL 20 and OL 30). The systemmay be implanted in a manner such that the IPG 1 and two leads 20, 30are disposed as illustrated in FIG. 19. The IPG 10 is capable offunctionally connecting to and communicating with a portable programmerand an external charging system for battery recharging, such as theheadset depicted in FIG. 8 and FIG. 15.

In this embodiment, the leads are constructed as described above and asdepicted in the drawings. The FPL 20 is approximately 26 cm in lengthfrom its proximal end 22 to its distal end 21. The FPL 20 has a distalnon-stimulating tip 23 of approximately 3 mm in length that abuts theFEA 25, which may have ten SME 24 uniformly disposed over approximately8 cm. This is followed by an inter-array interval 27 of approximately 4cm, then the PEA 26, which may include eight SME 24 uniformly disposedover approximately 6 cm, and finally a proximal lead segment 22 a thatends at the proximal end 22, where the lead transitions to the IPG 10and the lead internal wires 29, 38 connect to the ASIC 13.

In this embodiment, the occipital lead 30 may comprise a plastic bodymember 39 over which six SME 34 may be disposed uniformly overapproximately a 10 cm length of the lead, and the lead terminates inapproximately a 3 mm distal non-stimulating tip 33.

In this embodiment, the IPG 10 comprises the elements described aboveand depicted in the drawings, including an ASIC 13, a rechargeablebattery 12, and an antenna coil 11, which all may be housed in a commoninterior 15 that may include a medical grade metal can with plasticcover 14. In this embodiment the dimensions of the IPG 10 measured alongthe outer surface of the plastic cover 14 may be approximately 5 cm by 3cm by 0.5 mm.

When functioning, the electrodes of the terminal electrode array areprogrammed to function as anodes and cathodes, and such programming mayinclude such parameters as pulse amplitude, frequency and pulse width.The generated electrical pulse wave then passes from a connectedproximal surface metal contact, along the associated internal lead wire,and ultimately to its associated terminal surface metal electrode. Thecurrent then passes a short distance through the subcutaneous tissue toa contiguous, or nearby, electrode, whereby it passes back up the leadto its associated proximal metal contact, and then back to the pulsegenerator to complete the circuit. It is the generated pulse wavespassing through the subcutaneous tissue between two terminal electrodesthat stimulate the sensory nerves of the area. When active, the pulsegenerator is usually programmed to produce continuous series of pulsewaves of specified frequency, amplitude, and pulse width. It is thisseries of pulse waves actively stimulating a patient's locallyassociated nerves that underpins the therapeutic effect.

While this example neurostimulation system has been described forimplantation in the head and for head pain, it is capable of beingimplanted and used as a peripheral nerve stimulator over other regionsof the head and face than those described above, and also over otherperipheral nerves in the body.

Other Embodiments and Definitions

In one aspect, a system is provided for transferring power to, andcommunicating with, at least one body-implantable active device. In someembodiments the system includes an external power transfer systemassociated with an external device disposed outside of a body, operableto transfer power through a dermis layer to each body-implantable activedevice, and communicate data to and from each body-implantable activedevice, and also includes a power receiving system associated with eachbody-implantable active device, operable to receive power transferredfrom the external power transfer system, and communicate data to andfrom the external power transfer system.

In some embodiments the external power transfer system includes: atleast one transmit coil, each corresponding to a respectivebody-implantable active device; a driver circuit operable to drive theat least one transmit coil with an AC signal; a forward telemetrycircuit operable to modulate, responsive to a forward telemetry datainput signal, a corresponding data signal within the AC signal; and aback telemetry circuit operable to generate, responsive to a data signalmodulated within the AC signal, a corresponding back telemetry dataoutput signal.

Each power receiving system respectively includes: a receive coil tunedto the resonant frequency of the corresponding transmit coil; a chargereceiving circuit coupled to the receive coil, said charge receivingcircuit operable in a first mode to receive power transferred from thecorresponding transmit coil to the receive coil when in proximitythereto, and operable in a second mode to detune the receive coil tosubstantially inhibit power transfer from the corresponding transmitcoil to the receive coil; a forward telemetry circuit coupled to thereceive coil, being operable to generate, responsive to a modulated datasignal coupled onto the receive coil, a corresponding forward telemetrydata output signal; and a back telemetry circuit coupled to the receivecoil, being operable to modulate, responsive to a back telemetry datainput signal, a corresponding data signal onto the receive coil.

In some embodiments the external power transfer system is operable tocommunicate data to each power receiving system in both the first andsecond modes, and each power receiving system is operable to receivedata communicated from the external power transfer system in both thefirst and second modes. In some embodiments each power receiving systemis operable to communicate data to the external power transfer system inboth the first and second modes, and the external power transfer systemis operable to receive data communicated from each power receivingsystem in both the first and second modes. In some embodiments the backtelemetry circuit is further operable to de-tune the receive coil inaccordance with a serial bit-stream corresponding to the back telemetrydata input signal, and thereby modulate the corresponding data signalonto the receive coil, and the corresponding data signal modulated ontothe receive coil is communicated to the external power transfer systemas a corresponding data signal modulated within the AC signal.

In some embodiments the external power transfer system includes a singletransmit coil corresponding to a single body-implantable active device.

In some embodiments the driver circuit and the at least one transmitcoil comprise a resonant amplifier circuit.

In some embodiments each body-implantable active device ishead-locatable. In some embodiments each body-implantable active devicecomprises a neurostimulation pulse generator. In some embodiments theexternal power transfer system is disposed within a headset, and eachtransmit coil is co-locatable with the respective receive coil of theassociated body-implantable active device.

In some embodiments the external power transfer system includes aseries-connected plurality of transmit coils, each corresponding to arespective body-implantable active device, and the driver circuit isoperable to drive the series-connected plurality of transmit coils withthe AC signal. In some embodiments each body-implantable active devicecomprises a respective head-locatable neurostimulation system, and theexternal device disposed outside of a body comprises a headset chargingand control device operable to charge and communicate with eachrespective head-locatable neurostimulation system. In some embodimentseach body-implantable active device further comprises a battery, and abattery charging circuit coupled to the charge receiving circuit forreceiving the power transferred from the external power transfer system,and providing the received power as a charging current for the battery.In some embodiments each body-implantable active device is operable inthe first mode to receive power from the external power transfer systemand provide the received power as the charging current for the battery,and operable in the second mode to substantially inhibit power transferfrom the external power transfer system when battery charging iscomplete or no longer desired.

In another aspect, a system is provided for charging and communicatingwith at least two body-implanted active devices (BIADs), each with abattery. In some embodiments, the system includes an external chargingsystem disposed outside of the body for transferring charging energy tothe body and facilitating transmission of data to, and reception of datafrom, the body-implanted active devices, and also includes a chargereceiving system associated with each of the body-implanted activedevices for receiving energy transferred from the external chargingsystem and facilitating transmission of data to, and reception of datafrom, the external charging system.

In some embodiments, the external charging system includes: a pluralityof transmit coils disposed in series, each corresponding to a respectiveone of the body-implanted active devices; a driver circuit operable todrive the series-connected transmit coils with an AC signal; a datatransmitter circuit operable to modulate a data signal within the ACsignal; and a data receiver circuit operable to receive a data signalmodulated within the AC signal. Each of the charge receiving systemsincludes: a receive coil tuned to the resonant frequency of anassociated one of the transmit coils for receiving energy therefrom whenin proximity thereto; a charge receiving circuit coupled to the receivecoil, said charge receiving circuit operable in a first charging mode toreceive energy transferred from the associated transmit coil to thereceive coil, and operable in a second charging mode to detune thereceive coil to inhibit transfer of energy from the associated transmitcoil to the receive coil; a data receiver circuit operable to receivedata from the receive coil in both the first and second modes; and adata transmitter circuit operable to transmit data to the receive coilin both the first and second modes. The external charging system isoperable to transmit data to each of the associated charge receivingsystems, and receive data from each of the associated charge receivingsystems, in both the first and second charging modes.

In some embodiments, each of the body-implanted active devices ishead-located. In some embodiments, each of the body-implanted activedevices is subcutaneous within the body. In some embodiments, each ofthe body-implanted active devices includes an implanted pulse generator.In some embodiments, the external charging system is disposed within aheadset, and each transmit coil is co-locatable with the respectivereceive coil of the associated body-implanted active device. In someembodiments, the external charging system includes only one driver forthe two or more series-connected transmit coils. In some embodiments,the driver circuit, together with the two or more series-connectedtransmit coils, comprises a resonant amplifier circuit.

In some embodiments, a first one of the at least two body-implantedactive devices comprises a first implanted head-located neurostimulationsystem; a second one of the at least two body-implanted active devicescomprises a second implanted head-located neurostimulation system; andthe external charging system comprises a headset charging and controldevice operable to charge and communicate with both the first and secondimplanted head-located neurostimulation systems.

In another aspect a method is provided for wirelessly charging andcommunicating with an implantable medical device. In some embodimentsthe method includes: enabling periodic excitation of a resonant invertercircuit disposed within an external control device (ECD), the resonantinverter circuit having a first primary load coil that is operativelyinductively coupled with a first secondary load coil of a first resonantrectifier circuit disposed within a first implantable medical device(IMD), the resonant inverter circuit and the first resonant rectifiercircuit together operable as a resonant DC-DC converter circuit at afirst resonant frequency; gating the periodic excitation of the resonantinverter circuit in accordance with a forward serial data stream to becommunicated from the ECD to the first IMD; rectifying, using a firsthalf-wave rectifier circuit within the first resonant rectifier circuit,induced voltage transients of a first polarity to generate a chargingvoltage to power a battery charging circuit within the first IMD; andrectifying, using a second half-wave rectifier circuit within the firstresonant rectifier circuit, induced voltage transients of a secondpolarity opposite the first polarity, to generate within the first IMD afirst data signal corresponding to the forward serial data stream.

In some embodiments the gating includes: disabling the periodicexcitation during each bit position of the forward serial data streamhaving a first digital state; and enabling the periodic excitationduring each bit position of the forward serial data stream having asecond digital state opposite the first digital state.

In some embodiments the forward serial data stream has a bit ratecorresponding to a lower frequency than the first resonant frequency byat least a factor of 20. In some embodiments the first data signalwithin the first IMD corresponds to a peak value of the instantaneousper-cycle induced voltage transients of the second polarity.

In some embodiments the values of the first data signal above a firstthreshold level correspond to one of the first and second digital statesof the forward serial data stream, and values of the first data signalbelow the first threshold level correspond to the other of the first andsecond digital states of the forward serial data stream.

In some embodiments the method further includes: de-tuning, within thefirst IMD, the first secondary coil together with the first rectifiercircuit, to reduce the quality factor (Q) of the first resonantrectifier circuit with regard to induced transitions of the firstpolarity and to thereby reduce induced current coupled from the firstprimary coil to the first secondary coil, the de-tuning performed tocommunicate information from the first IMD to the ECD; and sensing,within the ECD, changes in current through the first primary coilresulting from the de-tuning of the first secondary coil by the firstIMD, to thereby detect the information communicated by the first IMD.

In some embodiments the method further includes disabling, in responseto receiving information communicated by the first IMD, the periodicexcitation to thereby cause resonant operation of the resonant invertercircuit to decay and ultimately cease, and to consequently turn off thebattery charging circuit within the first IMD.

In some embodiments the sensing comprises: generating, within the ECD, afirst waveform corresponding to instantaneous per-cycle current flowingthrough the first primary load coil; and detecting changes in peak valueof the first waveform to thereby detect the information communicated bythe first IMD.

In some embodiments the de-tuning is performed to indicate the first IMDbattery charging is complete.

In some embodiments: the information comprises a reverse serial datastream to be communicated from the first IMD to the ECD; the de-tuningis performed during each bit position of the reverse serial data streamhaving a first digital state, and the de-tuning is not performed duringeach bit position of the reverse serial data stream having a seconddigital state opposite the first digital state. In some embodiments thereverse serial data stream has a bit rate corresponding to a lowerfrequency than the first resonant frequency by at least a factor of 20.

In some embodiments the method further includes generating, in the ECD,a waveform corresponding to instantaneous per-cycle current flowingthrough the first primary load coil. In some embodiments the periodicexcitation comprises pumping current into the resonant inverter circuitduring a portion of each resonant cycle, beginning at a timecorresponding to a predetermined percentage of peak per-cycle currentflowing through the first primary load coil, and continuing for apredetermined duration.

In some embodiments the first IMD comprises an implantable head-locatedneurostimulation system. In some embodiments the ECD comprises a headsetcharging and control device for the implantable head-locatedneurostimulation system.

In some embodiments: the resonant inverter circuit comprises a Class Einverter circuit having an excitation coil coupled between a DC inputvoltage and a switch device; and the first resonant rectifier circuitcomprises a first Class E rectifier circuit; and wherein the Class Einverter circuit and the first Class E rectifier circuit are togetheroperable as an isolated Class E DC-DC converter circuit at the firstresonant frequency. In some embodiments the method further includesvarying the DC input voltage for the Class E inverter circuit to limitpower coupled to the first IMB and to thereby increase efficiency ofbattery charging within the first IMB. In some embodiments the methodfurther includes varying the DC input voltage for the Class E invertercircuit, in response to information received from the first IMB, tolimit voltage drop across a voltage regulator circuit within the firstIMB to thereby limit power dissipation within the first IMD.

In some embodiments: the Class E inverter circuit includes a secondprimary load coil in series with the first primary load coil, the secondprimary load coil operatively inductively coupled with a secondary loadcoil of a second Class E rectifier circuit disposed within a second IMD,the Class E inverter circuit and the first and second Class E rectifiercircuits together are operable as isolated Class E DC-DC convertercircuits at the first resonant frequency; and the method furtherincludes: gating the periodic excitation of the Class E inverter circuitin accordance with a forward serial data stream to be transmitted fromthe ECD to one or both of the first IMB and second IMD; rectifying,using a first half-wave rectifier circuit within the second IMD, inducedvoltage transients of the first polarity to generate a charging voltageto power a battery charging circuit within the second IMD; andrectifying, using a second half-wave rectifier circuit within the secondIMD, induced voltage transients of the second polarity, to generatewithin the second IMB a first data signal corresponding to the forwardserial data stream.

In some embodiments the method further includes: de-tuning, within thefirst IMD, the first secondary coil together with the first rectifiercircuit, to reduce the quality factor (Q) of the first resonant Class Erectifier circuit with regard to induced transitions of the firstpolarity and to thereby reduce induced current coupled from the firstprimary coil to the first secondary coil, the de-tuning performed atfirst times to communicate first information from the first IMB to theECD; de-tuning, within the second IMD, the second secondary coiltogether with the second rectifier circuit, to reduce the quality factor(Q) of the second resonant Class E rectifier circuit with regard toinduced transitions of the first polarity and to thereby reduce inducedcurrent coupled from the second primary coil to the second secondarycoil, the de-tuning performed at second times to communicate secondinformation from the second IMD to the ECD, wherein the second times maybut need not overlap the first times; and sensing, within the ECD,changes in current through the series combination of the first andsecond primary coils resulting from either or both of the de-tuning ofthe first secondary coil by the first IMD and the de-tuning of thesecond secondary coil by the second IMD, to thereby detect either orboth of the first information communicated by the first IMD and thesecond information communicated by the second IMD.

In some embodiments the first IMD comprises a first implantablehead-located neurostimulation system; the second IMD comprises a secondimplantable head-located neurostimulation system; and the ECD comprisesa headset charging and control device operable to charge and communicatewith both the first and second implantable head-located neurostimulationsystems.

While certain embodiments described herein may reference body-implantedactive devices having an onboard battery, such a battery is notrequired, as the described charge delivery systems may be utilized tocharge a battery within the body-implanted device (if present), and/orto power the body-implanted device, particularly if such body-implanteddevice does not include a battery.

Certain embodiments may incorporate an adjustable voltage generationcircuit (e.g., a buck/boost circuit as shown in FIG. 8 and FIG. 11) thatutilizes a local power supply voltage, such as a battery voltage, togenerate a VBOOST voltage that is typically higher in voltage than thelocal power supply. However, the VBOOST voltage in certain embodimentsmay be higher or lower than the local power supply voltage, dependingupon the battery voltage, the desired energy transfer to thebody-implanted active devices, and other factors.

As used herein, “exemplary” is used interchangeably with “an example.”For instance, an exemplary embodiment means an example embodiment, andsuch an example embodiment does not necessarily include essentialfeatures and is not necessarily preferred over another embodiment. Asused herein, “coupling” includes direct and/or indirect coupling ofcircuit components, structural members, etc.

Certain embodiments disclosed herein may be described as including anexternal charging system (or external charge transfer system) forcharging (or transferring charge to) one or more implantable devices.Strictly speaking, in the described embodiments using a transmit coiland a receive coil, energy is stored per cycle as a magnetic field inthe transmit coil, and some of this energy is transferred per cycle bymagnetic induction to the receive coil. In other words, energy istransferred over a certain duration of time from the transmit coil tothe receive coil, and the rate of such energy transfer is power.However, the words “energy” and “power” are frequently used somewhatinterchangeably when describing a magnetic induction circuit, since acircuit that transfers power (i.e., at a certain rate) also transfers acorresponding amount of energy over a duration of time. As such,disabling power transfer also likewise disables energy transfer whendisabled for a certain period of time. Moreover, reducing power transferalso likewise reduces energy transfer over a period of time. For thisreason, in context there is seldom confusion between usage of thephrases “transferred energy” and “transferred power”, or between thephrases “received energy” and “received power,” as it is usually clearin context whether the reference is to total transfer over a duration oftime, or to an instantaneous rate of transfer.

The phrases “power transfer” or “energy transfer” may also be somewhatinformally referred to as “charge transfer” because such transferredcharge may be for delivering power, in the form of a current (i.e.,moving electronic charge) at a certain voltage, to operate circuitrywithin the implantable device, in addition to (or instead of) charging asupercapacitor, battery, or other charge storage device within theimplantable device. Consequently, as used herein, an external chargingsystem may also be viewed as an external charge transfer system or anexternal power transfer system, and references herein to an externalcharging system, an external charge transfer system, and an externalpower transfer system may be used interchangeably with no specificdistinction intended unless clear in the context of such use, even if nocharge storage device is “charged” in a given embodiment. Such externalcharging, charge transfer, or power transfer systems may also be viewedas an external control system or device. Similarly, a charge receivingsystem may also be viewed as a power receiving system, and referencesherein to a charge receiving system and a power receiving system may beused interchangeably with no specific distinction intended unless clearin the context of such use.

Regarding terminology used herein, it will be appreciated by one skilledin the art that any of several expressions may be equally well used whendescribing the operation of a circuit including the various signals andnodes within the circuit. Any kind of signal, whether a logic signal ora more general analog signal, takes the physical form of a voltage level(or for some circuit technologies, a current level) of a node within thecircuit. Such shorthand phrases for describing circuit operation usedherein are more efficient to communicate details of circuit operation,particularly because the schematic diagrams in the figures clearlyassociate various signal names with the corresponding circuit blocks andnodes.

An insulated gate field effect transistor (IGFET) may be conceptualizedas having a control terminal which controls the flow of current betweena first current handling terminal and a second current handlingterminal. Although IGFET transistors are frequently discussed as havinga drain, a gate, and a source, in most such devices the drain isinterchangeable with the source. This is because the layout andsemiconductor processing of the transistor is frequently symmetrical(which is typically not the case for bipolar transistors). For anN-channel IGFET transistor, the current handling terminal normallyresiding at the higher voltage is customarily called the drain. Thecurrent handling terminal normally residing at the lower voltage iscustomarily called the source. A sufficient voltage on the gate(relative to the source voltage) causes a current to therefore flow fromthe drain to the source. The source voltage referred to in N-channelIGFET device equations merely refers to whichever drain or sourceterminal has the lower voltage at any given point in time. For example,the “source” of the N-channel device of a bi-directional CMOS transfergate depends on which side of the transfer gate is at the lower voltage.To reflect this symmetry of most N-channel IGFET transistors, thecontrol terminal may be deemed the gate, the first current handlingterminal may be termed the “drain/source”, and the second currenthandling terminal may be termed the “source/drain”. Such a descriptionis equally valid for a P-channel IGFET transistor, since the polaritybetween drain and source voltages, and the direction of current flowbetween drain and source, is not implied by such terminology.Alternatively, one current-handling terminal may arbitrarily deemed the“drain” and the other deemed the “source”, with an implicitunderstanding that the two are not distinct, but interchangeable. Itshould be noted that IGFET transistors are commonly referred to asMOSFET transistors (which literally is an acronym for“Metal-Oxide-Semiconductor Field Effect Transistor”), even though thegate material may be polysilicon or some material other than metal, andthe dielectric may be oxynitride, nitride, or some material other thanoxide. The casual use of such historical legacy terms as MOS and MOSFETshould not only be interpreted to literally specify a metal gate FEThaving an oxide dielectric.

Regarding power supplies, a single positive power supply voltage (e.g.,a 3.0 volt power supply) used to power a circuit is frequently named the“V_(DD)” power supply. In an integrated circuit, transistors and othercircuit elements are actually connected to a V_(DD) terminal or a V_(DD)node, which is then operably connected to the V_(DD) power supply. Thecolloquial use of phrases such as “tied to V_(DD)” or “connected toV_(DD)” is understood to mean “connected to the V_(DD) node”, which istypically then operably connected to actually receive the V_(DD) powersupply voltage during use of the integrated circuit. The referencevoltage for such a single power supply circuit is frequently called“V_(SS).” Transistors and other circuit elements are actually connectedto a V_(SS) terminal or a V_(SS) node, which is then operably connectedto the V_(SS) power supply during use of the integrated circuit.Frequently the V_(SS) terminal is connected to a ground referencepotential, or just “ground.” Generalizing somewhat, the first powersupply terminal is frequently named “V_(DD)”, and the second powersupply terminal is frequently named “V_(SS).” Historically thenomenclature “V_(DD)” implied a DC voltage connected to the drainterminal of an MOS transistor and V_(SS) implied a DC voltage connectedto the source terminal of an MOS transistor. For example, legacy PMOScircuits used a negative V_(DD) power supply, while legacy NMOS circuitsused a positive V_(DD) power supply. Common usage, however, frequentlyignores this legacy and uses V_(DD) for the more positive supply voltageand V_(SS) for the more negative (or ground) supply voltage unless, ofcourse, defined otherwise. Describing a circuit as functioning with a“V_(DD) supply” and “ground” does not necessarily mean the circuitcannot function using other power supply potentials. Other common powersupply terminal names are “V_(CC)” (a historical term from bipolarcircuits and frequently synonymous with a +5 volt power supply voltage,even when used with MOS transistors which lack collector terminals) and“GND” or just “ground.”

Moreover, implementation of the disclosed devices and techniques is notlimited by CMOS technology, and thus implementations can utilize NMOS,PMOS, and various bipolar or other semiconductor fabricationtechnologies. While the disclosed devices and techniques have beendescribed in light of the embodiments discussed above, one skilled inthe art will also recognize that certain substitutions may be easilymade in the circuits without departing from the teachings of thisdisclosure. Also, many circuits using NMOS transistors may beimplemented using PMOS transistors instead, as is well known in the art,provided the logic polarity and power supply potentials are reversed. Inthis vein, the transistor conductivity type (i.e., N-channel orP-channel) within a CMOS circuit may be frequently reversed while stillpreserving similar or analogous operation. Moreover, other combinationsof output stages are possible to achieve similar functionality.

The various techniques, structures, and methods described above arecontemplated to be used alone as well as in various combinations. Itshould be understood that the drawings and detailed description hereinare to be regarded in an illustrative rather than a restrictive manner,and are not intended to be limiting to the particular forms and examplesdisclosed. On the contrary, included are any further modifications,changes, rearrangements, substitutions, alternatives, design choices,and embodiments apparent to those of ordinary skill in the art, withoutdeparting from the scope of the invention as defined by the claims inthis application or in any application claiming priority to thisapplication. Thus, it is intended that such claims be interpreted toembrace all such further modifications, changes, rearrangements,substitutions, alternatives, design choices, and embodiments.

What is claimed is:
 1. A system for transferring power from an external power transfer system (EPTS) to at least one body-implantable active device (BIAD) through a dermis layer, said system comprising: an EPTS for being disposed external to a dermis layer of a body; and a BIAD for being disposed beneath the dermis layer of the body; the EPTS including: a transmit coil; a variable voltage generator circuit operable to generate on an output thereof a variable DC voltage; and a resonant driver circuit coupled to the variable DC voltage output, and operable to drive the transmit coil with a resonant current at a resonant frequency; the BIAD including: a receive coil tuned to the resonant frequency of the transmit coil and operable to inductively receive power therefrom when in proximity thereto; and a power receiving circuit coupled to the receive coil and operable to deliver the received power to circuitry within the BIAD; wherein the EPTS is operable to adjust the variable DC voltage to modulate energy stored in the resonant driver circuit each resonant cycle and to modulate available transmitted power that is receivable by the BIAD.
 2. The system as in claim 1 wherein: the EPTS further comprises a back telemetry receive circuit for receiving back telemetry information from the BIAD; and the EPTS is further operable to control the variable voltage generator circuit in response to back telemetry information received from the BIAD.
 3. The system as in claim 1 wherein: the EPTS further comprises a current sensing circuit for detecting a change in transmitted power received by the BIAD; and the EPTS is further operable to control the variable voltage generator circuit in response to detecting a change in transmitted power received by the BIAD.
 4. The system as in claim 1 wherein: the variable voltage generator circuit comprises a buck/boost circuit operable to generate the variable DC voltage output having a magnitude controllable over a range extending above and below a battery voltage powering the variable voltage generator circuit.
 5. The system as in claim 1 wherein: the resonant driver circuit further comprises an excitation input operable to pump energy into the resonant driver circuit each resonant cycle.
 6. The system as in claim 5 wherein the resonant driver circuit comprises: an excitation coil and a switch device coupled in series between an upper power supply node and a lower power supply node, wherein the switch device is operable, responsive to a control input thereof, to substantially impress the variable DC voltage across the excitation coil during a portion of each resonant cycle to thereby store in the excitation coil an amount of energy that varies in accordance with the variable DC voltage, and to decouple the excitation coil from the lower power supply node during a remaining portion of each resonant cycle to thereby deliver the stored energy to the transmit coil.
 7. The system as in claim 6 wherein the resonant driver circuit further comprises: a capacitor coupled between a first node and an output node of the resonant driver circuit, said first node disposed between the excitation coil and the switch device.
 8. The system as in claim 6 wherein the resonant driver circuit further comprises: a buffer circuit having an output coupled to the switch device control input, wherein the buffer circuit includes a boosted supply greater than a battery voltage powering the EPTS.
 9. The system as in claim 8 wherein: the buffer circuit comprises an input coupled to the excitation input of the resonant driver circuit.
 10. The system as in claim 9 further comprising: a triggerable oscillator circuit having an input coupled to receive a trigger signal, and operable to generate an excitation signal on an output thereof which is coupled to the excitation input of the resonant driver circuit.
 11. The system as in claim 10 wherein the triggerable oscillator circuit is operable to cause the excitation signal to oscillate, at a self-oscillation frequency, in the absence of periodic assertions of the trigger signal.
 12. The system as in claim 1 wherein: the BIAD comprises a head-locatable neurostimulation system; the EPTS is disposed within a headset charging and control device operable to charge and communicate with the head-locatable neurostimulation system; and the transmit coil is co-locatable with the receive coil.
 13. The system as in claim 12 wherein: the resonant driver circuit comprises a Class E inverter circuit having an excitation coil coupled between a first node and a first power supply node conveying the variable DC voltage, having a switch device coupled between the first node and a reference power supply node, and having a capacitor coupled between the first node and an output node thereof; and the power receiving circuit comprises a Class E resonant rectifier circuit; wherein said Class E inverter circuit and said Class E resonant rectifier circuit are together operable as an isolated Class E DC-DC converter circuit at the resonant frequency.
 14. A system for transferring power from an external power transfer system (EPTS) to at least one body-implantable active device (BIAD) through a dermis layer, said system comprising: an EPTS for being disposed external to a dermis layer of a body; and a BIAD for being disposed beneath the dermis layer of the body; the EPTS including: a transmit coil; a variable voltage generator circuit operable to generate on an output thereof a variable DC voltage responsive to a voltage control signal received on an input thereof; and a resonant driver circuit operable to drive the transmit coil with a resonant current at a resonant frequency, said resonant driver circuit having an upper power supply node coupled to the variable DC voltage output, and having a lower power supply node coupled to a reference power supply voltage; the BIAD including: a receive coil tuned to the resonant frequency of the transmit coil and operable to inductively receive power therefrom when in proximity thereto; and a power receiving circuit coupled to the receive coil and operable to deliver the received power to circuitry within the BIAD; wherein the EPTS is operable to adjust the variable DC voltage to modulate energy stored in the resonant driver circuit each resonant cycle and to thereby modulate available transmitted power that is receivable by the BIAD.
 15. The system as in claim 14 wherein: the EPTS further comprises a back telemetry receive circuit for receiving back telemetry information from the BIAD; and the EPTS is further operable to control the variable voltage generator circuit in response to back telemetry information received from the BIAD.
 16. The system as in claim 14: wherein the variable voltage generator circuit comprises a buck/boost circuit operable to generate the variable DC voltage output having a magnitude controllable over a range extending above and below a battery voltage powering the variable voltage generator circuit; and wherein the resonant driver circuit further comprises: an excitation coil and a switch device coupled in series between the upper power supply node and the lower power supply node, wherein the switch device is operable, responsive to a control input thereof, to substantially impress the variable DC voltage across the excitation coil during a portion of each resonant cycle to thereby store in the excitation coil an amount of energy that varies in accordance with the variable DC voltage; and a capacitor coupled between a first node and an output node of the resonant driver circuit, said first node disposed between the excitation coil and the switch device.
 17. The system as in claim 16 wherein the resonant driver circuit further comprises: a buffer circuit having an input coupled to an excitation input of the resonant driver circuit, having an output coupled to the switch device control input, and having a boosted local power supply greater in magnitude than a battery voltage powering the EPTS.
 18. The system as in claim 16 wherein: the resonant driver circuit comprises a Class E inverter circuit; and the power receiving circuit comprises a Class E resonant rectifier circuit; wherein said Class E inverter circuit and said Class E resonant rectifier circuit are together operable as an isolated Class E DC-DC converter circuit at the resonant frequency.
 19. The system as in claim 16 further comprising at least a second BIAD, and wherein: the EPTS includes a series-connected plurality of transmit coils, each corresponding to a respective BIAD; and the resonant driver circuit is operable to drive the series-connected plurality of transmit coils with the resonant current at the resonant frequency.
 20. The system as in claim 19 wherein: each respective BIAD comprises a respective head-locatable neurostimulation system; the EPTS is disposed within a headset charging and control device operable to charge and communicate with each respective head-locatable neurostimulation system; and each transmit coil is co-locatable with the corresponding receive coil. 